In a 25-year period, 144 patients with proliferating epithelial ovarian tumours were treated at the King George V Memorial Hospital. These tumours were classified according to the World Health Organisation (WHO) Histological Classification of Ovarian Tumours and subsequently divided into 4 grades of proliferation, again on histological criteria. The tumours were staged at laparotomy in accord with the recommendations of the International Federation of Gynecology and Obstetrics (FIGO). Follow-up data, analysed by a life-table method, were correlated against histological type of tumour, histological grade of proliferation, clinical/laparotomy stage, and mode of surgical therapy. Stage 1 proliferating tumours may be treated by surgery alone, including unilateral salpingo-oophorectomy in selected cases. Stage 2 and Stage 3 tumours should be treated similarly to invasive ovarian carcinomas of the same stage, despite their overall favourable prognosis.