This report describes 2 cases of spontaneous malignant neoplasia within the sex skin of aged female chimpanzees. In both cases, the initial presentation resembled nonhealing traumatic wounds to the sex skin, with different degrees of infection, ulceration, and tissue necrosis. Histopathology of the lesions confirmed the diagnosis of squamous cell carcinoma in one case and of adenocarcinoma with metastasis in the other. Advanced age and previous trauma likely contributed to the development of the neoplasias in both cases; long-term sun exposure may also have contributed to the development of the squamous cell carcinoma. To our knowledge, these 2 cases represent the first reports of sex skin neoplasia in chimpanzees.