Page.xaml

<UserControl x:Class="ScrollBarVisibilityEx.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
   Height="400" Width="300" >
    <!--<snippet1>-->
    <StackPanel Height="400" Width="300">
        <ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Disabled">
            <Grid VerticalAlignment="Top" HorizontalAlignment="Left">
                <Rectangle Fill="Green" Width="450" Height="200"></Rectangle>
                <TextBlock Margin="10,10,10,10">
                    Auto. The horizontal scroll bar is shown if the content is wider than the viewport.
                </TextBlock>
            </Grid>
        </ScrollViewer>
        <ScrollViewer HorizontalScrollBarVisibility="Hidden">
            <Grid>
                <Rectangle Fill="Blue" Width="450" Height="200" />
                <TextBlock Margin="10,10,10,10">
                    Hidden. The horizontal scroll bar is hidden even if the content is wider than the viewport.
                </TextBlock>
            </Grid>
        </ScrollViewer>
    </StackPanel>
    <!--</snippet1>-->
</UserControl>