Ileocolonoscopy with biopsy of the ileum, ileocecal valve and cecum was performed on 32 patients (22 males, 10 females) with juvenile chronic arthritis (JCA) with pauciarticular onset. Mean age at onset of disease was 12 years. Ankylosing spondylitis (AS) was diagnosed in 13 patients; the other 19 cases were classified as reactive arthritis with recurrent or persistent pauciarticular synovitis. Twenty-two patients (68%) were HLA-B27 positive; 8 patients (25%) carried the HLA-Bw62 antigen. Ileocolonoscopy was performed 6 months to 32 years after the initial manifestation of the disease (mean : 9 years). Fourteen patients had macroscopic lesions of the ileum and ileocecal valve although only 8 of these had a history of intestinal complaints. Twenty-six patients (81%) presented histological signs of gut inflammation. Most of the gut abnormalities were classified as active chronic or Crohn-like lesions (19/26). Only 7 patients had acute or bacterial enteritis-like lesions. Acute lesions were seen in only one patient with AS. All but 2 patients with sacroiliitis, in whom signs of gut inflammation were found, had active chronic lesions. All the 8 HLA-Bw62 positive patients had histological evidence of gut inflammation. Only chronic or Crohn-like lesions were found. In the majority of patients with JCA with pauciarticular onset, gut inflammation was found on ileum biopsy. Some of their lesions are related to Crohn's disease, and the presence of the HLA-Bw62 antigen could predispose to the arthritis seen in these cases.