Is gastrointestinal fistula a complication of crohn's disease?

Yes.: A fistula is a connection between two distinct organs or structures. Some people with Crohn's disease are prone to fistula formation, whereby the affected portion of the intestine can bore a hole ito an adjacent organ (intestine, bladder, vagina) or the skin. These fistulae almost always require definitive surgery.

Yes: Crohns results in full thickness[transmural] inflammation with can cause abscess or fistula.