Treatment of severe acne with isotretinoin in patients with inflammatory bowel disease. Four patients with inflammatory bowel disease and severe cystic acne were treated with isotretinoin. Two patients had a successful course of treatment without any gastrointestinal side-effects. One patient had two episodes of profuse rectal bleeding that were probably related to pre-existing haemorrhoids. The fourth patient had a flare-up of his Crohn's disease after starting isotretinoin. 