The gestational history of 512 women with multiple sclerosis revealed that the risk of MS-onset, exacerbation, or progression was two to three times as high during the 6 months after childbirth as during pregnancy. Using a progression-index as a measure of prognosis (disability divided by duration), the speed of deterioration was comparable for women who became pregnant and those who did not. An apparent but insignificant trend toward better prognosis for women with pregnancies after MS-onset was most likely due to their younger age at onset. The natural course of pregnancy and childbirth was comparable among women pregnant before and during the disease. There was no evidence of an increased frequency of congenital malformations in the offsprings.