@kitebuggy I saw your code last night and that it was missing a layout on the central widget of the main window but wasn't sure whether that would produce the behaviour you see. So that you know: look at @Christian-Ehrlicher's two screenshots. The first one is your original code. Look at the Object Explorer pane at the right: notice that centralWidget has a "red no-entry sign" on it. Whenever you see that in Designer it indicates you are missing a layout on that widget. See how in the second screenshot that has disappeared. So look out for that when designing. (Having said this: I'm not quite sure what is going on with your QGroupBox widget: that still shows a "red no-entry" even though you have added an explicit QVBoxLayout on it. I tend not to add explicit layout objects unless I really need them, you can also set a layout on a widget by right-clicking on it and selecting Layout > (once it has at least one child widget, it's disabled before that) and I do that whenever possible. i am still not sure whether that way or adding an explicit layout as a child result in the same code/behaviour....)