We studied retrospectively a group of 53 patients with Crohn's disease, diagnosed between 18 and 21 years of age. They had all undergone a thorough medical evaluation at age 17 before military service. They thus served as a unique group in whom the natural course of the disease, duration of signs and symptoms before diagnosis, and delay in diagnosis could be assessed. Other than a more frequently elicited history of nonspecific mild recurrent abdominal pain in childhood in the patient group, medical history, physical growth, sexual development, and laboratory parameters of inflammation did not differ in the patient group and the healthy control group. Crohn's disease in this group of young adults is likely one of acute onset and did not begin as an exacerbation of a more subtle and prolonged process.