diff --git a/BeWo/Converter/ValidationConverter.cs b/BeWo/Converter/ValidationConverter.cs
index 6ee6613a2..37f55b2e2 100644
--- a/BeWo/Converter/ValidationConverter.cs
+++ b/BeWo/Converter/ValidationConverter.cs
@@ -18,7 +18,7 @@ namespace BeWo.Converter
 		{
 			if(value is string val_str && parameter is ValidationType val_type)
 			{
-				return Validator.IsValid(val_type, val_str);
+				return GkvValidator.IsValid(val_type, val_str);
 			}
 
 			return null;
diff --git a/BeWo/Converter/ValidationToTooltipConverter.cs b/BeWo/Converter/ValidationToTooltipConverter.cs
index 1aa37ac78..50a9d77b4 100644
--- a/BeWo/Converter/ValidationToTooltipConverter.cs
+++ b/BeWo/Converter/ValidationToTooltipConverter.cs
@@ -22,7 +22,7 @@ namespace BeWo.Converter
 
 			if (value is bool val_bool && parameter is ValidationType val_type)
 			{
-				return val_bool ? null : Validator.InvalidTooltipTxt(val_type);
+				return val_bool ? null : GkvValidator.InvalidTooltipTxt(val_type);
 			}
 
 			return "xxx";
diff --git a/BeWo/ViewModel/OrganisationVM.cs b/BeWo/ViewModel/OrganisationVM.cs
index bd5785db1..5289a71a8 100644
--- a/BeWo/ViewModel/OrganisationVM.cs
+++ b/BeWo/ViewModel/OrganisationVM.cs
@@ -713,8 +713,8 @@ namespace BeWo.ViewModel
 		}
 
 		public bool IsIKNumberValid
-			=> Validator.IsIKNumberValid(IKKrankenkasse)
-			&& Validator.IsLeistungserbringergruppeValid(Leistungserbringergruppe);
+			=> GkvValidator.IsIKNumberValid(IKKrankenkasse)
+			&& GkvValidator.IsLeistungserbringergruppeValid(Leistungserbringergruppe);
 
 		public string IKKrankenkasse
 		{
diff --git a/Service/DCEntityMapper/GkvAbrechnungDC_GkvAbrechnung.cs b/Service/DCEntityMapper/GkvAbrechnungDC_GkvAbrechnung.cs
index f0339cd64..259bc9bbd 100644
--- a/Service/DCEntityMapper/GkvAbrechnungDC_GkvAbrechnung.cs
+++ b/Service/DCEntityMapper/GkvAbrechnungDC_GkvAbrechnung.cs
@@ -67,7 +67,7 @@ namespace BeWo.Service.DCEntityMapper
 				// Hole OrganisationLight
 				var orga = DAOFactory.GenericDAO.LoadByID<OrganisationLight>(orga_oid);
 				
-				if (!Validator.IsOrganisationInformationValid(orga))
+				if (!GkvValidator.IsOrganisationInformationValid(orga))
 				{
 					isReady = false;
 					tooltip = "Organisation ist nicht Gkv Ready";
diff --git a/Service/DCEntityMapper/InvoiceBaseDC_InvoiceBase.cs b/Service/DCEntityMapper/InvoiceBaseDC_InvoiceBase.cs
index 524adb4b4..186ee1148 100644
--- a/Service/DCEntityMapper/InvoiceBaseDC_InvoiceBase.cs
+++ b/Service/DCEntityMapper/InvoiceBaseDC_InvoiceBase.cs
@@ -146,8 +146,12 @@ namespace BeWo.Service.DCEntityMapper
                 pDataContract.CustomerOid = customer.Oid.Value;
                 pDataContract.CustomerFirstName = customer.Person.FirstName;
                 pDataContract.CustomerLastName = customer.Person.LastName;
-                var error = Validator.ValidateCustomer(customer.InsuranceNumber, customer.VersichertenStatus);
-                pDataContract.IsGkvValidError = error;
+
+                var error = GkvValidator.ValidateCustomer(customer.InsuranceNumber, customer.VersichertenStatus);
+                if (error is null)
+                    error = GkvValidator.ValidateInvoiceBase(pDataContract);
+
+				pDataContract.IsGkvValidError = error;
                 pDataContract.IsGkvValid = error is null;
             }
 
diff --git a/Service/ServiceImplementations/CustomerServiceImp.cs b/Service/ServiceImplementations/CustomerServiceImp.cs
index 44e2e6bff..e9117921d 100644
--- a/Service/ServiceImplementations/CustomerServiceImp.cs
+++ b/Service/ServiceImplementations/CustomerServiceImp.cs
@@ -852,7 +852,7 @@ namespace BeWo.Service.ServiceImplementations
 				IList<Organisation> list = DAOFactory.GenericDAO.GetAllActiveAndArchived<Organisation>();
 
 				list = list.Where(x => !x.GkvAusblenden &&
-					Validator.IsOrganisationInformationValid(x.IKDatenannahmestelle, x.IKKostentrager, x.IKKrankenkasse, x.BezDatenannahmestelle)).ToList();
+					GkvValidator.IsOrganisationInformationValid(x.IKDatenannahmestelle, x.IKKostentrager, x.IKKrankenkasse, x.BezDatenannahmestelle)).ToList();
 
 				return CreateCompactOrganisations(list);
 			}
diff --git a/Service/ServiceImplementations/GkvAccountingServiceImp.cs b/Service/ServiceImplementations/GkvAccountingServiceImp.cs
index ee582a6b0..a64a0ffc5 100644
--- a/Service/ServiceImplementations/GkvAccountingServiceImp.cs
+++ b/Service/ServiceImplementations/GkvAccountingServiceImp.cs
@@ -377,12 +377,12 @@ namespace BeWo.Service.ServiceImplementations
 				var manager = new DakotaManager();
 				var mandatordc = new OperationsServiceImp().GetMandator();
 
-				Validator.ValidateMandator(mandatordc);
+				GkvValidator.ValidateMandator(mandatordc);
 
 				var gkvAbrechnungDC = MapperFactory.GkvAbrechnungDC_GkvAbrechnung.MapToNewDC(gkvAbrechnung);
 				var orgadc = gkvAbrechnungDC.Organisation;
 
-				Validator.ValidateOrganisation(orgadc);
+				GkvValidator.ValidateOrganisation(orgadc);
 
 				var datenannahmestelle = orgadc.IKDatenannahmestelle;
 				var (datenaustauschreferenz, transfernummer) = GetNextDatenaustauschreferenzTransfernummer(gkvAbrechnung, datenannahmestelle);
@@ -416,7 +416,7 @@ namespace BeWo.Service.ServiceImplementations
 					var servicedc = MapperFactory.ServiceInvoiceDC_ServiceInvoice.MapToNewDC(service);
 					var customerdc = MapperFactory.CustomerDC_Customer.MapToNewDC(customer);
 
-					Validator.ValidateCustomer(customerdc);
+					GkvValidator.ValidateCustomer(customerdc);
 
 					manager.Add(servicedc, orgadc, customerdc, addressInfo, dat_short, tra_short);
 				}
diff --git a/Shared/Core/Validator.cs b/Shared/Core/GkvValidator.cs
similarity index 85%
rename from Shared/Core/Validator.cs
rename to Shared/Core/GkvValidator.cs
index 24acd3b4a..71d09dd21 100644
--- a/Shared/Core/Validator.cs
+++ b/Shared/Core/GkvValidator.cs
@@ -6,11 +6,12 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 
 namespace BS.Shared.Core
 {
-    public static class Validator
+    public static class GkvValidator
     {
 		public static bool? IsValid(ValidationType val_type, string val_str)
 		{
@@ -73,7 +74,7 @@ namespace BS.Shared.Core
             if (mandatordc == null)
                 throw new GkvException("Mandator ist null");
 
-            if (!Validator.IsIKNumberValid(mandatordc.IKLeistungserbringer))
+            if (!IsIKNumberValid(mandatordc.IKLeistungserbringer))
                 throw new GkvException($"Die IK Nummer des Leistungserbringers \"{mandatordc.IKLeistungserbringer}\" ist ungültig.");
         }
         public static void ValidateCustomer(CustomerDC customerDC)
@@ -110,16 +111,35 @@ namespace BS.Shared.Core
             if (error != null)
                 throw new GkvException(error);
         }
-        public static bool IsOrganisationInformationValid(IOrganisation orga)
+		public static string ValidateInvoiceBases(IEnumerable<IInvoiceBase> invoices)
+		{
+            foreach (var invoice in invoices)
+            {
+                if (ValidateInvoiceBase(invoice) is string error)
+                    return error;
+			}
+
+            return null;
+		}
+		public static string ValidateInvoiceBase(IInvoiceBase invoice)
+		{
+			if (!IsInvoiceNumberValid(invoice.InvoiceNumber))
+				return $"Rechnungsnummer \"{invoice.InvoiceNumber}\" ist ungültig";
+
+			return null;
+		}
+
+		public static bool IsOrganisationInformationValid(IOrganisation orga)
         {
             return IsOrganisationInformationValid(orga.IKDatenannahmestelle, orga.IKKostentrager, orga.IKKrankenkasse, orga.BezDatenannahmestelle);
-        }
-        public static bool IsOrganisationInformationValid(string ik_datenannahmestelle, string ik_kostentrager, string ik_krankenkasse, string bez_datenannahmestelle)
+		}
+		public static bool IsOrganisationInformationValid(string ik_datenannahmestelle, string ik_kostentrager, string ik_krankenkasse, string bez_datenannahmestelle)
             => IsIKNumberValid(ik_datenannahmestelle, ik_kostentrager, ik_krankenkasse) && IsBezDatenannahmestelleValid(bez_datenannahmestelle);
         public static bool IsIKNumberValid(params string[] iks)
             => iks?.All(IsIKNumberValid) ?? false;
 
-        public static bool IsBezDatenannahmestelleValid(string bez_datenannahmestelle)
+
+		public static bool IsBezDatenannahmestelleValid(string bez_datenannahmestelle)
 		{
             return !string.IsNullOrWhiteSpace(bez_datenannahmestelle);
         }
@@ -180,5 +200,11 @@ namespace BS.Shared.Core
 
             return true;
         }
+		public static bool IsInvoiceNumberValid(string invoiceNumber)
+		{
+			var pattern = @"^(?!.*[-/]{2})(?![-/])(?!.*[-/]$)[A-Za-z0-9]+(?:[/-][A-Za-z0-9]+)*$";
+
+            return Regex.IsMatch(invoiceNumber, pattern);
+		}
 	}
 }
diff --git a/Shared/Core/ValidatorExtended.cs b/Shared/Core/ValidatorExtended.cs
index e8b008b28..cfa066a1d 100644
--- a/Shared/Core/ValidatorExtended.cs
+++ b/Shared/Core/ValidatorExtended.cs
@@ -7,6 +7,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
+using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 
 namespace BS.Shared.Core
@@ -23,6 +24,8 @@ namespace BS.Shared.Core
 				error = "Unterschiedliche Rechnungspositionen";
 			else if (GetInvalidUnitDescription(invoiceBases) is IInvoiceItem invalid)
 				error = $"Ungültige Rechnungsposition: {invalid.ItemDescription}:{invalid.UnitDescription}";
+			else if (GetInvalidInvoiceNumber(invoiceBases) is IInvoiceBase invalid2)
+				error = $"Ungültige Rechnungsnummer: {invalid2.InvoiceNumber}";
 
 			if(error is string)
 				throw new GkvException(error, "Validierung");
@@ -71,5 +74,7 @@ namespace BS.Shared.Core
 
 			return null;
 		}
+
+		
 	}
 }
diff --git a/Shared/Interface/IInvoiceBase.cs b/Shared/Interface/IInvoiceBase.cs
index 905442066..db3a0cc8e 100644
--- a/Shared/Interface/IInvoiceBase.cs
+++ b/Shared/Interface/IInvoiceBase.cs
@@ -9,6 +9,7 @@ namespace BS.Shared.Interface
 	public interface IInvoiceBase
 	{
 		long? Oid { get; }
+		string InvoiceNumber { get; }
 		string InvoiceTitle { get; }
 		string InvoiceId { get; }
 		string SenderStreet { get; }
diff --git a/Shared/Shared.csproj b/Shared/Shared.csproj
index 0e7be8270..4b8736e97 100644
--- a/Shared/Shared.csproj
+++ b/Shared/Shared.csproj
@@ -151,7 +151,7 @@
     <Compile Include="Core\SecurityUtils.cs" />
     <Compile Include="Core\TokenUtils.cs" />
     <Compile Include="Core\Utilities\WebUtils.cs" />
-    <Compile Include="Core\Validator.cs" />
+    <Compile Include="Core\GkvValidator.cs" />
     <Compile Include="Core\DebugUtils.cs" />
     <Compile Include="Core\ImageUtils.cs" />
     <Compile Include="Core\PersonFilterEnum.cs" />