XAML:

<Window x:Class="ListCheckBox2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="785" FontSize="22" Loaded="Window_Loaded">
    <Grid>
        <Label Content="Liste" Height="43" HorizontalAlignment="Left" Margin="49,24,0,0" Name="labelAuswahl" VerticalAlignment="Top" Width="auto" />
        <ListBox Height="161" HorizontalAlignment="Left" Margin="57,63,0,0" Name="listBox1" VerticalAlignment="Top" Width="281" >
        </ListBox>
        <ListBox Height="161" HorizontalAlignment="Left" Margin="451,63,0,0" Name="listBox2" VerticalAlignment="Top" Width="281" />
        <Label Content="Auswahl" Height="43" HorizontalAlignment="Left" Margin="451,24,0,0" Name="label1" VerticalAlignment="Top" Width="auto" />
        <Button Content="_OK" Height="33" HorizontalAlignment="Left" Margin="244,245,0,0" Name="bnOk" VerticalAlignment="Top" Width="94" Click="bnOk_Click" />
    </Grid>
</Window>


CS:

        private void Window_Loaded(object sender, RoutedEventArgs e) {
            setGUI();
        }

        private void setGUI() {
            for (int i = 0; i < 100; i++) {
                ListBoxItem li = new ListBoxItem();
                CheckBox chk = new CheckBox();
                chk.Content = (i + 1) + ". Kontrollfeld";
                chk.Click += new RoutedEventHandler(chk_Click);
                li.Content = chk;
                listBox1.Items.Add(li);
            }
            labelAuswahl.Content = "Auswahl (0 Elemente ausgewählt)";
        }

        private void chk_Click(object sender, RoutedEventArgs e) {
            int summe = 0;
            listBox2.Items.Clear();
            foreach (ListBoxItem item in listBox1.Items) {
                CheckBox chkb = (CheckBox)item.Content;
                if (chkb.IsChecked == true) {
                    summe++;
                    listBox2.Items.Add(chkb.Content);
                }
            }
            labelAuswahl.Content = "Auswahl (" + summe
                + " Elemente ausgewählt)";
        }
        private void bnOk_Click(object sender, RoutedEventArgs e) {
            foreach (ListBoxItem item in listBox1.Items) {
                CheckBox chkb = (CheckBox)item.Content;
                if (chkb.IsChecked == true) {
                    MessageBox.Show(chkb.Content.ToString());
                }
            }

        }