Introduction: Limited information is available on the characteristics of longstanding Crohn's disease with onset in childhood or adolescence. Materials and Methods: In this retrospective study, 224 patients with pediatric-onset Crohn's disease were compared to a group of patients with disease diagnosed as adults. Results: More than 50% of the patients in the pediatric-onset group were followed for more than a decade, with a mean follow-up of 12.2 years. There were 96 male (42.9%) and 128 female (57.1%) patients. Most had disease diagnosed in adolescence. The female predominance, similar to adult-onset disease, was noted only among patients with disease diagnosed in adolescence (13-19 years), not in childhood. Disease most often involved both ileum and colon (128 of 224; 57.1%). Isolated ileal or colonic disease was less common. Upper gastrointestinal tract disease was present in 42 of 224 (18.8%) patients. The incidence of strictures (28.6%) and penetrating complications (46.4%) was similar to that of adults followed for the same period of time. Conclusion: In pediatric-onset Crohn's disease, female-predominance emerges during adolescence. Pediatric-onset disease is more extensive than adult-onset disease. When followed for an extended period of time, it has high rates of disease complexity, with strictures and penetrating complications similar to adult-onset disease. (C) 2004 Lippincott Williams Wilkins.