Concerns have been raised recently about the possible association between superovulation and ovarian cancer. In order to contribute to the limited literature on this important issue, two cases of ovarian tumours in women who had undergone multiple ovulation inductions are presented. In the first case, the patient had secondary anovulatory infertility. She was treated with human menopausal gonadotrophin (HMG) alone and in combination with clomiphene citrate or buserelin for six cycles. She then underwent ovarian stimulation with buserelin/HMG in the long protocol for in-vitro fertilization (IVF) and embryo transfer. In preparation for a new IVF/embryo transfer attempt, 8 months later, the screening ultrasound revealed a cystic formation of the left ovary and an enlargement of the right. During laparotomy, both ovaries were found to bear large tumours (approximately 6 x 5 x 4 cm) which were removed. Histological examination showed that they were epithelial tumours (serous-papillary cystadenomas) of borderline malignancy. The patient conceived spontaneously 1.5 years after the operation. In the second case, the patient presented with secondary anovulatory infertility. She underwent ovulation induction with clomiphene/HMG and with buserelin/HMG in the long protocol, and intra-uterine insemination with husband's spermatozoa and conceived (singleton pregnancy). She was delivered by Caesarean section, during which a cystic tumour of the left ovary was removed. Histological examination revealed a benign mucous cystadenoma of the ovary.(ABSTRACT TRUNCATED AT 250 WORDS)