Bonsoir,
a adapter et tester pour trois colonnes
Private Sub Worksheet_Change(ByVal Cellule As Excel.Range)
If Cellule.Column = 1 Or 3 Then
If Application.WorksheetFunction. _
CountIf(Range("A1:c12"), Cellule.Value) > 1 Then
MsgBox "HOLA,Je suis déja inscrit "
Cellule.Value = ""
Cellule.Select
End If
End If
End Sub
A +