The solitary fibrous tumor, of rare mesodermal origins, primarily affects the pleura and occasionally occursin the peritoneum and at nonserosal sites. Although this is a pathologically well established entity, it isfrequently confused radiologically and pathologically with other tumors of mesenchymal origin. We report one case of a solitary fibrous tumor in the retroperitoneum. The 15X10X7cm mass, lacated in the left perirenal space just above the left kidney, had relatively homogeneous consistency and was well-delineated from surrounding organs inCT and MR images. It showed intense, gradual, centripetal enhancement during dynamic scans, and partially unenhanced areas which matched the high signal intensity portions in T2 weighted MR images, pathologically correlated to myxoid degeneration. Although not specific, when a large, well-delineated mass of strong contrast enhancement with lack of massive necrosis is encountered, solitary fibrous tumor must be included in the differential diagnosis of a refroperitoneal soft tissue mass.