Two young women taking phenytoin because of symptomatic brain metastases are described. Both patients, one with end-stage lung cancer and the other in complete remission after intensive chemotherapeutic treatment of a choriocarcinoma, became pregnant while using oral contraceptives in combination with phenytoin. One patient had the child, but died a year after the metastases became apparent, in the other the pregnancy was terminated. When prescribing phenytoin, attention should be paid to fertility--even in patients with end-stage cancer or after intensive, possibly sterilising, chemotherapeutic treatment.