We present a patient with primary retroperitoneal synovial sarcoma which showed a monophasic fibrous pattern, the fourth such case to be described, and a review of the literature. Synovial sarcoma cells in the present case were stained positive for cytokeratin and epithelial membrane antigen (EMA), of which histology was differentiated from other spindle cell sarcoma with similar light microscopic features. Retroperitoneal synovial sarcoma is usually treated surgically, however only one of 16 cases identified in the literature survived five years after resection. Due to the high fatality rate, physicians should be alerted to the possibility of this disorder in the differential diagnosis of an abdominal mass.