The course of pregnancy in 97 women with ulcerative colitis was studied over a 12-year period. During this period they had 173 pregnancies and delivered 136 children. There were two gemellary deliveries. Nine women had a spontaneous and 16 an induced abortion, of which 4 were performed on therapeutic indication. For a woman with ulcerative colitis the risk of an exacerbation of the bowel disease was 32% per year in her fertile years, whereas it was 34% per year during pregnancy. This difference is not statistically significant. As compared with women with an inactive bowel disease, women in whom the disease was active at the start of pregnancy had a small but significantly greater risk of spontaneous abortion and premature delivery. The frequency of malformations, prematurity, and neonatal hyperbilirubinaemia was not higher in the children of ulcerative colitis mothers than in those of healthy mothers. Treatment with sulphasalazine, salazosulphadimidine, and corticosteroids had no influence on the course and outcome of pregnancy. Birth length and weight of the children of mothers with ulcerative colitis equalled those for children of healthy mothers. In conclusion, pregnancy does not necessitate any change in the usual medical treatment of ulcerative colitis. Women with ulcerative colitis should be advised preferably to conceive at a time when their bowel disease is inactive. Generally, ulcerative colitis constitutes no indication for induced abortion.