Dedifferentiated chondrosarcoma is a biphasic tumour, comprising well-differentiated chondrosarcoma and an anaplastic non-cartilaginous sarcoma juxtaposed but distinct from each other. Two cases of dedifferentiated chondrosarcoma, one primary and one recurrent, demonstrated muscle differentiation when studied with monoclonal antibodies to muscle specific actin, desmin and myoglobin. One of the tumours was also positive for cytokeratin, identified by AE1/AE3 and CAM 5.2 antibodies. Our findings are consistent with the concept that these tumours are capable of diverse patterns of morphological and immunophenotypic differentiation.