Private Sub ExistWS()
  Dim ws As Worksheet, Exist As Boolean
 
  For Each ws In Worksheets
    If ws.Name = "Neues Blatt" Then
      Exist = True
      Exit For
    End If
  Next
 
  If Not Exist Then
    Set ws = Sheets.Add(After:=Worksheets(Worksheets.Count))
    ws.Name = "Neues Blatt"
  End If
End Sub

Gruß
Marcus