Primary peritoneal carcinomas are rare, highly aggressive malignant neoplasms containing both sarcomatous and carcinomatous elements. Surgical debulking is the mainstay of treatment for primary peritoneal carcinomas. Systemic chemotherapy is advised in all cases because of the early spreading of these tumours. We report on a case of primary peritoneal carcinosarcoma occurring in a 22-year-old woman.