Background: Nevoid basal cell carcinoma syndrome (NBCC) is an autosomal dominant disorder characterized by developmental abnormalities and neoplasms including basal cell carcinoma (BCC) and sarcomas (i.e. leiomyosarcoma, rhabdomyosarcoma, and fibrosarcoma). Primary cutaneous carcinosarcoma(PCC), a rare tumor composed of malignant epithelial and mesenchymal components, has never been previously described in association with this syndrome. Case report: A 61- year- old Hispanic man with a history of NBCC presented with a 4 cm nodule on the right proximal medial thigh. Pathologic findings: Areas of typical BCC merged with intersecting fascicles of large atypical spindle cells that stained for vimentin and were negative for actin, desmin, CD- 34, and S- 100 protein. Scattered bizarre solitary cytokeratin- positive epithelioid cells were embedded within the fibrocytic proliferation. Conclusions: Several carcinosarcomas have been reported to contain BCC as the malignant epithelial component, but to our knowledge, this is the first report of PCC associated with NBCC. Mutation in patched tumor suppressor gene on chromosome 9q occurs in BCCs of NBCC, and aberrancies on chromosome 9q are also reported in some carcinosarcomas. It is possible that the known genetic defect on chromosome 9 in this patient contributed to the development of carcinosarcoma. Background: Nevoid basal cell carcinoma syndrome (NBCC) is an autosomal dominant disorder characterized by developmental abnormalities and neoplasms including basal cell carcinoma (BCC) and sarcomas (ie leiomyosarcoma, rhabdomyosarcoma, and fibrosarcoma). Primary cutaneous carcinosarcoma (PCC), a rare tumor composed of malignant epithelial and mesenchymal components, has never been previously described in association with this syndrome. Case report: A 61-year-old Hispanic man with a history of NBCC presented with a 4 cm nodule on the right proximal medial thigh. Pathologic findings : Areas of typical BCC merged with intersecting fascicles of large atypical spindle cells that stained for vimentin and were negative for actin, desmin, CD-34, and S-100 protein. Scattered bizarre solitary cytokeratin- positive epithelioid cells were embedded within the fibrocytic proliferation Conclusions: Several carcinosarcomas have been reported to contain BCC as the malignant epithelial component, but to our knowledge, this is the first report of PCC associated with NBCC. Mutation in patched tumor suppressor gene on chromosome 9q occurs in BCCs of NBCC, and aberrancies on chromosome 9q are also reported in some carcinosarcomas. It is possible that the known genetic defect on chromosome 9 in this patient contributed to the development of carcinosarcoma.