Sarcomatoid component can occur in all histological subtypes of renal cell carcinoma but most commonly accompanies chromophobe renal cell carcinoma. The majority of the sarcomatoid components consist of malignant fibrous histiocytoma, fibrosarcoma or undifferentiated sarcoma areas. Heterologous differentiation in the form of osteosarcoma or rhabdomyosarcoma is very rarely encountered. We report a very rare case of a chromophobe renal cell carcinoma with osteosarcomatous differentiation that presented as a retroperitoneal mass. Renal cell carcinoma with sarcomatoid change should be always kept in mind when a retroperitoneal mass with sarcomatoid differentiation is encountered.