Malignant fibrous histiocytoma is a mesenchymal tumour which can involve the genitourinary organs primarily or by secondary extension. Both conditions are rare. We report four cases of retroperitoneal malignant fibrous histiocytoma involving the kidney by local extension. Diagnosis was difficult because of diverse, non-specific clinical features and may only be reached at operation or post mortem. Prognosis is poor. Although en bloc tumour resection with nephrectomy was possible in two patients, they returned with recurrences.