Although onset is most common in the third decade of life, more than one third of IBD cases are diagnosed before age sixteen, and these younger patients, especially with Crohn's disease, are increasing in Western countries. Recent studies in the United Kingdom, Sweden and the United States report an incidence of 5-7 new cases of IBD every year per 100,000 subjects < 16 years of age, with an increasing trend over the last two decades.