Cystic ovarian teratomas are common tumours. Malignant melanoma developing in a teratoma, however, is an extremely rare diagnosis. A 49-year-old woman with a history of weight loss and abdominal distension was referred to UCLH. She underwent laparotomy and bilateral salpingo-oophorectomy for a large right ovarian tumour. Histopathology revealed a malignant melanoma and carcinoid tumour in the right ovarian teratoma and an endometrioid adenocarcinoma in the left ovary. Subsequent vaginal hysterectomy revealed complex atypical hyperplasia in the endometrium. An extraovarian primary maelanoma could not be found. At this time the patient remains alive and well with no indication of recurrence.