C# – how do I prevent mousewheel-scrolling in my combobox?

Use the MouseWheel event for your ComboBox:

void comboBox1_MouseWheel(object sender, MouseEventArgs e) {
    ((HandledMouseEventArgs)e).Handled = true;
}

Note: you’ll have to create event in code:

comboBox1.MouseWheel += new MouseEventHandler(comboBox1_MouseWheel);