Symptoms, tumour morphology and clinical course were reviewed in 26 women treated at the department of obstetrics and gynaecology of the University of Cologne between 1965 and 1986 for granulosa cell tumours of the ovary. At the time of diagnosis 8 women were in a pre- and 18 in a postmenopausal state. The most common symptoms were irregular haemorrhages, in rare cases lower abdominal pain. Effects of raised estrogen stimulation were seen in 80% of patients. In 24 pre-operative patients, a lower abdominal tumour was diagnosed. 20 patients had lesions of stage I, 5 of stage III and one of stage IV. 21 tumours exceeded 5 cm median diameter. Polymorphic tumours were seen in 16 cases. 14 tumours had a high mitotic activity. Hysterectomy and bilateral salpingoovariectomy were performed in most cases, followed by additional irradiation in 9 and by chemotherapy in 4 cases. Only 3 patients were treated by unilateral salpingoovariectomy. To date 14 patients have no evidence of disease, one suffers from tumour progression and 9 died of the tumours. 2 women died for other reasons. The 5-year survival rate is 70%, the 10-year survival rate 64%. Old age, late progression of tumour stage, tumour diameter exceeding 5 cm, polymorphic tumours and high mitotic index correlated to the worsening prognosis. However, a poor result was also seen in monomorphic tumours with low mitotic activity. The nature of granulosa cell tumours can not be predicted by clinical or morphological criteria. Therefore it is suggested, that all granulosa cell tumours should be considered as malignant.