OBJECTIVE: To examine the incidence and prevalence of pediatric inflammatory bowel disease (IBD) during 1996-2006 in a community-based health-care delivery system. STUDY DESIGN: Members of Kaiser Permanente Northern California aged 0 to 17 years with IBD were identified by use of computerized medical information with confirmation obtained through review of the medical record. RESULTS: The average annual incidence of IBD per 100000 was 2.7 (95% confidence interval [CI], 2.3-3.1) for Crohn’s disease (CD) and 3.2 (CI, 2.8-3.6) for ulcerative colitis (UC). During the 11-year study period, the annual incidence per 100000 increased from 2.2 to 4.3 for CD (P = .09) and from 1.8 to 4.9 for UC (P < .001). The ratio of incident CD cases to incident UC cases was 0.9 in non-Hispanic whites, 1.6 in African Americans (P = .12), 0.3 in Hispanics (P < .001) and 0.4 in Asians (P = .04). The average length of enrollment during the 11-year study period exceeded 8 years. The point prevalence on December 31, 2006, per 100000 was 12.0 for CD (CI, 9.6-14.4) and 19.5 (CI, 16.5-22.6) for UC. CONCLUSIONS: In this population the incidence of UC increased significantly by 2.7-fold and CD increased 2.0-fold without reaching statistical significance. Hispanic and Asian children had development of UC more often than CD, suggesting possible etiologic differences across racial and ethnic groups.