you can use a macro to force the values into a single list
Sub Validation() Dim a$, el As Range ' SET THE LIST RANGE, YOU CAN USE MORE THAN 2 Dim rng1 As Range, rng2 As Range 'DEFINE THE CELLS USED FOR THE LIST, NAMED RANGE OR INDIRECT CAN BE USED Set rng1 = Range("List1") Set rng2 = Range("List2") 'COLLECT VALUES FROM LISTS For Each el In rng1 a = a & el.Value & "," Next For Each el In rng2 a = a & el.Value & "," Next ' SET DESTIANTION OF DATA VALIDATION RULE With Range("A1").Validation .Delete .Add Type:=xlValidateList, Formula1:=a End With Set rng1 = Nothing Set rng2 = Nothing End Sub The only drawback is, the macro would need to be run each time you added a value to your list, you could put this in via a workbook change maybe