Arthritis occurred in 23 of 136 (17 per cent) children and teenagers with inflammatory bowel disease, in 18 of 86 (21 per cent) patients with ulcerative colitis, and 5 of 50 (10 per cent) with granulomatous bowel disease. Eighteen children had peripheral arthritis which characteristically affected only a few large joints and was of brief duration and benign outcome. Five boys had spondylitis which was progressive and inseparable clinically from ankylosing spondylitis. Occurrence of joint manifestations was not associated with severity of bowel disease. Anemia and growth retardation occurred frequently. Mucocutaneous lesions were associated with peripheral arthritis but not with spondylitis. No patient had iridocyclitis. The possibility of bowel disease should be considered in children presenting with arthritis, particularly if gastrointestinal complaints, mucocutaneous lesions, anemia, or growth retardation are associated with pauciarticular arthritis. Peripheral arthritis is benign and regresses with improvement of underlying bowel disease but spondylitis is progressive and requires recognition and management for prevention of deformity.