In an earlier epidemiological study covering a 12-year period from 1956-67, a gradual increase in the number of patients with Crohn's disease was found. A study of the subsequent 6 years, from 1968-73, is now presented. The mean incidence of the disease for this period is 5.0, compared with 3.1 for the preceding 6 years, 1962-67. As in the earlier 12-year series, the increasing incidence can be attributed largely to an increase in the 15-29 year age group. During the period 1956-67, the disease occurred almost as frequently in men as in women. In the 6-year period now presented, there is a predominance of women, especially over the age of 35.