Primary leiomyosarcoma is an extremely rare entity constituting only 0.5-1% of all invasive renal tumors. It is frequently diagnosed on histological examination because it does not have any specific diagnostic features clinically and radiologically. At times, it is difficult to differentiate leiomyosarcoma from the sarcomatoid renal cell carcinoma even in histopathology as both the tumors have spindle-shaped atypical cells. Moreover, some epithelial markers can be present in pure smooth muscle sarcomas, while some smooth muscle markers are positive in carcinomas. Hence, a diagnosis of primary renal leiomyosarcoma should be made with caution. Since the prognosis for a renal sarcoma is particularly poor, differentiation from sarcomatoid renal cell carcinoma is necessary. The diagnostic challenge of one such tumor is discussed.