In the present study, 93 consecutive women, 20-40 years of age, referred to our clinic from 1976-85 with Graves' disease, were examined with respect to a possible relation between onset of disease and previous pregnancy. An increased relative risk of 6.5 (3.8-11.0, 95% confidence interval) of developing Graves' disease within one year following delivery was found. After excluding the nulliparous women, almost 2 out of 3 women who developed Graves' disease in the principal child-bearing age of 20-35 years had a postpartum onset, suggesting an important role of immunomodulatory events following delivery for the development of this disease in young women. Future studies will ascertain to which extent the recognition of postpartum Graves' disease has implications on the choice of therapy in this group of women.