Surface epithelial-stromal cell tumors are the most common neoplasms of the ovary but occurrence of a serous adenocarcinoma and an adult granulosa cell tumor in the same ovary is an unusual incident. In the present case report we describe this very uncommon occurrence in the ovary of a 50-year-old woman. The patient suffered abdominal distention and was referred to the state hospital where a 5x3 cm multilocular cystic lesion was observed on abdominal CT. Total abdominal hysterectomy with salpingo-oophorectomy and omentectomy was performed. Microscopy revealed an adult granulosa cell tumor and a serous papillary adenocarcinoma in the left ovary. Immunohistochemical staining with inhibin alpha and pancytokeratin confirmed the diagnosis.