Familial cylindromatosis (Brooke-Spiegler syndrome) is a rare autosomal dominant inherited disease characterized by the development of adnexal tumors, mostly cylindromas, but also trichoepitheliomas and spiradenomas. Malignant tumors may occur, usually with the features of a cylindrocarcinoma. The authors describe the case of a 75-year-old woman with the Brooke-Spiegler syndrome who presented with multiple nodules of the scalp, face, and trunk. In 1997 she underwent surgical excision of the entire forehead and scalp with skin grafting. Histologic examination revealed multiple cylindromas, some with areas of spiradenoma and one with an extensive adenomatous component; some trichoepitheliomas were also evident. In 2002, a nodule of the trunk suddenly increased in size and became painful. The lesion was excised and histologic and immunohistochemical evaluation revealed a malignant cutaneous biphasic tumor extending into the subcutis, consisting of a major portion with the features of an adnexal carcinoma and of a minor one of atypical spindle cells. Biphasic malignant skin tumors are rare and only a limited number have been described, none in association with the Brooke-Spiegler syndrome. The authors discuss the morphogenesis of the folliculosebaceous-apocrine unit from which the tumors in this syndrome derive, and the pivotal role of mesenchymal cells in determining the process. Since the Brooke-Spiegler syndrome is characterized by a germline mutation in the CYLD oncosuppressor gene, a biphasic tumor in this setting may represent a true carcinosarcoma.