OBJECTIVE: To assess the incidence and location at diagnosis of inflammatory bowel disease in children and adolescents in northern France between 1988 and 1999. METHODS: A 12-year prospective population-based study was conducted by gastroenterologists and pediatric gastroenterologists of northern France (1,312,141 children <17 years of age). RESULTS: From 1988 to 1999, 509 cases of childhood inflammatory bowel disease were recorded (7.2% of all inflammatory bowel disease cases in Northern France): 367 Crohn disease, 122 ulcerative colitis and 20 indeterminate colitis. The mean standardized incidence was 3.1/10(5) for inflammatory bowel disease as a whole (2.3 for Crohn disease, 0.8 for ulcerative colitis and 0.12 for indeterminate colitis). Crohn disease location at diagnosis was: small bowel and colon (71%), colon only (10%) and small bowel only (19%). Location of initial ulcerative colitis was: proctitis (11%), left colitis (57%) and pancolitis (32%). Although ulcerative colitis incidence remained stable (0.8), Crohn disease incidence increased from 2.1 in 1988 to 1990 to 2.6 in 1997 to 1999 (P = 0.2). CONCLUSIONS: The incidence of Crohn disease in the children of northern France showed an increasing trend (20%; not significant) during the 12-year period while the incidence of ulcerative colitis remained stable. In the entire population(children and adults)the incidence of Crohn disease increased significantly (+23%; P < 0.001), while the incidence of ulcerative colitis decreased (-17%; P < 0.0001).