Hi seantera,

May be this is not the best solution but you can use this in the sheets selection change event.

This assuming that your listbox is in the cell "E1". Please change to suit yours. And you need to check at the VBE immidiate window to see the correct name for your drop down list. Here I only have one drop down list, so the name is "Drop Down 1).

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim s As Shape
Dim BtnWidth As Single
With ActiveCell
Select Case .Address(False, False)
Case "E1"
If .Validation.Type = xlValidateList Then
Set s = ActiveSheet.Shapes("Drop Down 1")
BtnWidth = s.Width - .Width
s.Width = 150
s.Left = .Left + .Width - s.Width + BtnWidth
Set s = Nothing
End If
End Select
End With
End Sub

Best regards,