The clinical manifestations of Crohn's disease (CD) and ulcerative colitis (UC) are highly variable, with significant diversity in phenotypes of the diseases. This diversity may manifest as a difference in age of onset. Pediatric-onset disease may present differently and have a different natural history, with ramifications for disease management. Clear evidence exists at present that pediatric-onset UC may be different than adult-onset UC. The primary difference in disease phenotype is extent of disease. Approximately 60-70% of patients with pediatric-onset UC present with pancolitis, as opposed to approximately 20-30% in adults. Patients are more likely to have severe disease and become steroid-dependent. CD may be affected by an age gradient. There is an inverse linear relationship between age and colonic CD, the younger the patient, the more likely is the patient to have colonic CD. This inverse relationship is true through age 10. In addition, pediatric patients are more likely to have upper gastrointestinal involvement than their adult peers. Comparing adult and pediatric phenotypes is fraught with methodological obstacles. Disease behavior, with the exception of growth failure, seems to parallel disease behavior in adults. Patients with growth retardation are a high risk group for complications and should be managed as such.