Forty-four Asian immigrants in Birmingham and 44 age- and sex-matched white Caucasians with ulcerative colitis were compared to investigate the existence of any ethnic differences in the pattern of disease. Asian immigrants demonstrated a male preponderance of 2:1, and compared to the matched Caucasians there was a higher incidence of presenting eosinophilia and a milder course of disease, with more patients experiencing only a single initial attack. In spite of this clinical difference, total or subtotal colitis was the commonest pathological type in both white Caucasians and Indians, whereas in Pakistanis localized distal disease predominated. All ethnic groups suffered the same overall complication rate (55%) which is at variance with the experience of low complication rates in India. The age of onset of ulcerative colitis was related to age at immigration with a mean interval of 11 years. Although in some respects Asian immigrants share the disease pattern of the indigenous population, the observed significant differences could be of importance with regard to pathogenesis.