 <p>When the combobox loads initially, no item is selected. It then sets the selected item to "Keine Angabe" based on the IsSelected property. This then causes the selection change event to fire. If you remove it, you will see the event is not fired.</p> <p>You can re-use the method for other comboboxes by casting the sender to the combobox type: See below:</p> <pre><code>private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e) { var combobox = sender as ComboBox; combobox.BorderBrush = new SolidColorBrush(new Color { R = 204, G = 204, B = 204, A = byte.MaxValue }); } </code></pre>