We present a retrospective study of granulosa cell tumours and thecomas encountered in one hospital between 1970 and 1995. There were 17 granulosa cell tumours and 17 thecomas. The size of the granulosa cell tumours varied from 3 cm to 30 cm in diameter, and no correlation was found between size and evidence of invasion. There was also no correlation between either mitotic counts or histological pattern and evidence of invasion. Evidence of oestrogen production was found in 12/17 granulosa cell tumours (two with endometrial carcinoma and 10 with endometrial hyperplasia) and in 9/17 of the thecomas (two with endometrial carcinoma and seven with endometrial hyperplasia). Thecomas are regarded as benign tumours, but granulosa cell tumours are characterised by a long natural history with a significant capacity to recur years after an apparent clinical cure. It is therefore important that patients with these tumours are followed up indefinitely.