checked listbox control

There are two of these controls in my windows application.
checking the items in the first one should cause the items in the second control to populate.
At present I use the mouse_leave event on the first control to trigger the event to populate the second control.
Is this the proper event I should use? I do not think the selectedIndex event is the correct one for this purpose either. Any suggestions please?
Thanks

Use ItemCheck event like this:

vb.net Code:

Private Sub CheckedListBox1_ItemCheck( _
    ByVal sender As Object, _
    ByVal e As System.Windows.Forms.ItemCheckEventArgs _
) Handles CheckedListBox1.ItemCheck
 
    If e.NewValue = CheckState.Checked Then
        MessageBox.Show("Item checked !")
    Else
        MessageBox.Show("Item Un-checked !")
    End If
End Sub