To check all items in .NET, you can use the following code snippet: Code for VB: Dim i as Integer For i = 0 To myCheckedListBox.Items.Count – 1 myCheckedListBox.SetItemChecked(i, True) Next Code for C#: for( int i = 0; i < myCheckedListBox.Items.Count; i++ ) { myCheckedListBox.SetItemChecked(i, true); }