Sub essai()
Set f = Sheets("nouveau")
Set d1 = CreateObject("Scripting.Dictionary")
For Each c In Range(f.[a2], f.[a65000].End(xlUp))
d1(c.Value) = "nouveau"
Next c
Set f = Sheets("connu")
For Each c In Range(f.[a2], f.[a65000].End(xlUp))
If d1.exists(c.Value) Then d1(c.Value) = "les deux" Else d1(c.Value) = "connu"
Next c
Sheets("difference").[d2].Resize(d1.Count, 1) = Application.Transpose(d1.keys)
Sheets("difference").[e2].Resize(d1.Count, 1) = Application.Transpose(d1.items)
End Sub