or

public class MyComboBox : Telerik.Windows.Controls.RadComboBox{}<Style x:Key="MyComboBoxStyle" TargetType="Controls:MyComboBox"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="Controls:MyComboBox" > <Grid x:Name="LayoutRoot"> <Grid.ColumnDefinitions> <ColumnDefinition Width="*"/> <ColumnDefinition Width="Auto"/> </Grid.ColumnDefinitions> <telerik:RadComboBox x:Name="PART_RadComboBox" Grid.Column="0" ItemsSource="{TemplateBinding ItemsSource}" SelectedItem="{TemplateBinding SelectedItem}" SelectedValue="{TemplateBinding SelectedValue}" DisplayMemberPath="{TemplateBinding DisplayMemberPath}" SelectedValuePath="{TemplateBinding SelectedValuePath}"> </telerik:RadComboBox> <telerik:RadButton x:Name="PART_RadButton" Grid.Column="1" Content="+"/> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style>