A case of leiomyosarcoma of the retroperitoneum with rhabdomyoblastic areas which developed in a 59-year-old woman is reported. The tumor was composed mostly of spindle cells immunoreactive with desmin and smooth muscle actin antisera. In the lesion there were no fewer than five patches constituted by large pleomorphic elements which reacted with antidesmin, sarcomeric actin and myoglobin antisera. These dual features were interpreted as the result of a divergent differentiation of neoplastic cells.