It'll depend on what kind of button and what kind of combobox.
It could be as simple as:
Option Explicit
Private Sub CommandButton1_Click()
With Me.ComboBox1
.Visible = Not .Visible
End With
End Sub
This actually toggles the visibility.
If you just want to hide it, use this line:
.Visible = false
> Is it possible for me to create a macro so that when I click a button, a
> combo box is hidden?
>
> I'm using Excel 2007 and Vista Home Premium if that helps
>
> Thanks

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Dave Peterson