A prospective, population-based study was carried out from 1980 to 1984 and again from 1991 to 1995 to determine the incidence of ulcerative colitis in an urban area in Germany. Patients with proctitis were excluded from this analysis. 74 (1980-84) and 76 (1991-95) patients newly diagnosed with ulcerative colitis were identified. A slight rise in the age- and sex-standardized incidence rate from 2.4/10(5) in 1980-84 (95% CI 1.8/10(5) to 3.0/10(5)) to 3.0 (95% CI 2.4/10(5) to 3.7/10(5)) in 1991-95 was primarily due to a significant increase of the disease in young woman. A male preponderance in the earlier time period was hereby leveled out. There were no differences in the extent of the disease and the severity of symptoms. However, the time from onset of symptoms to diagnosis was reduced from a median of nine months in the 1980s to two months in the more recent period.