To assess the incidence of ulcerative colitis and proctitis in a defined migrant population, a retrospective, epidemiological community study was performed in the London Borough of Tower Hamlets from 1972 to 1989. The population of 164,000 includes 28,000 Bangladeshis. Potential cases were identified from hospital departments of pathology and medical records. There were 107 cases of ulcerative colitis in Europeans and 5 in Bangladeshis. There were 74 and 2 cases of proctitis in these communities, respectively. The mean standardised incidence of ulcerative colitis in Bangladeshis (1.8 cases/10(5)/year) was marginally lower than in Europeans (6.2 cases/10(5)/year, Z = 0.7, n.s.). The mean standardised incidence of proctitis in Bangladeshis was 0.6 cases/10(5)/year and in Europeans 3.2 cases/10(5)/year (Z = 0.6 n.s.). Anatomical extent of colitis was similar in all ethnic communities, although complications were less likely in minority groups. These findings suggest that the incidence of ulcerative colitis and proctitis in Bangladeshis, in Britain, is amongst the lowest in the world.