[en] A first prospective epidemiological study of IBD was conducted in the area of Liege. The duration of the study was short taking into account the small size of the population (1 million inhabitants). Therefore we carried out a 3 years prospective study. METHOD: Private and public gastroenterologists completed a questionnaire for each new case they diagnosed between 01.06.1993 and 31.05.1996. RESULTS: During that period 270 IBD patients were identified: 137 (51%) had Crohn's disease (CD), 111 (41%) had ulcerative colitis (UC) including 32 proctitis (29% of UC) and 22 (8%) had unclassified colitis. The mean annual incidence per 10(5) was 4.5 for CD and 3.6 for UC. The female/male ratio was 1,6 for CD and 0,5 for UC. The median age at the time of diagnosis was 30 years for CD and 39 years for UC. The mean time between the onset of symptoms and the diagnosis was 6,5 months for CD and only 4,8 months for UC. Family history of IBD was found in 15% of patients with CD and in 7% of UC. CONCLUSIONS: These data show a high incidence of IBD in the area of Liege. These results confirm those reported during the first year of the prospective study which were similar to those observed in North-western France. Contrary to the other countries of Northern Europe, the incidence of UC is lower than the one of CD. Belgium appears to be a privileged country to undertake a national register and to study epidemiological aspects of IBD.