The first X-files film was produced between two seasons of the TV show. I've been racking my brains and cannot think of another example where a motion picture has been produced while the show is still on the air. Sex and the city, ST:TNG films etc all occured after their series went off air*.
What other examples are there?
* Worf appears in First Contact while DS9 is still on air but that's not quite the same thing.
What other examples are there?
* Worf appears in First Contact while DS9 is still on air but that's not quite the same thing.