To examine the possibility that cytotoxic drugs may cause sterility or congenital malformations in the offspring of women of childbearing age who are cured of cancer a study was conducted of the obstetric histories of 445 long term survivors treated in this unit with chemotherapy for gestational trophoblastic tumours between 1958 and 1978. After completing treatment 97% of those who wished for a pregnancy (49% of all women studied) conceived and 86% had at least one live birth. All these women had received methotrexate. Of the 47 women who wished to conceive and whose combination therapy included cyclophosphamide, 37 (79%) had a live birth. Women who received three or more drugs were less likely to have a live birth than those who received methotrexate alone or with only one other drug (p less than 0.001). There was no statistically significant excess of congenital malformations. These results are strong evidence that the cytotoxic drug regimens used in this unit for treating gestational trophoblastic tumours are compatible with the preservation of fertility in most women and not associated with any increase in congenital abnormalities.