Joe,
This way deselectes any selected item:

ListBox1.SetSelected(0, False)

It's up to you when you trigger the event. For instance, you can place
a simple button named "clear" then:
Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnClear.Click
ListBox1.SetSelected(0, False)
End Sub

Hi Joe,

The ListBox does not natively support this functionality, but depending on
how the items are displayed (multiple columns etc) you can set
SelectedItems.Clear() if you find out you have clicked outside any item.

You need to either handle the MouseDown or the MouseClick event.  Using
MouseDown in a ListBox with blank space at the bottom you can determine if
the mouseposition is below the last item

   void listBox1_MouseDown(object sender, MouseEventArgs e)
   {
       if (e.Y > listBox1.ItemHeight * listBox1.Items.Count)
           listBox1.SelectedItems.Clear();
   }

This won't work if you have custom drawn the items using variable heights.

If you want to deselect an item if you click to the right of it you then
need to find the correct item and figure out if e.X is on the right side of
the item's bounds.