A 40-year-old Turkish man on busulphan treatment for chronic myeloid leukaemia was hospitalized with steroid resistant (up to 100 mg prednisolone/24 h for over 4 weeks) colitis. On the basis of concomitant orogenital ulceration and unusual, deep punched out ulcers in the colon and smaller ulcers in the terminal ileum, Behçet's disease of the bowel, manifesting as ileocolitis, was diagnosed. Leukaemic infiltration, Crohn's colitis, neutropenic colitis and infectious colitis were excluded by histology and cultures. Treatment with colchicine 2 mg/day improved the orogenital ulcers but with only minor improvement of the colitis. Thalidomide treatment (400 mg/day), however, dramatically improved the colitis within 7 days: fever and diarrhoea disappearing. Colonoscopy after 4 weeks of treatment revealed previously giant ulcers practically healed.