Dedifferentiated liposarcoma represents a both morphologically and biologically fascinating lesion in which transition from low-grade to high-grade nonlipogenic morphology within a well-differentiated liposarcoma is observed. A peculiar form of dedifferentiated liposarcoma characterized by a nonlipogenic component with a meningothelial-like whorling pattern of growth and metaplastic bone formation has been described. A 59-year-old man presented with a pelvic retroperitoneal mass measuring 13x10x8 cm. Histopathologically the mass consisted almost entirely of a dedifferentiated nonlipogenic component with meningothelial-like whorling pattern, metaplastic cartilage and bone. Dedifferentiated liposarcoma with meningothelial-like whorling pattern has rarely been encountered. Here, we report this case because of the problems in differential diagnosis especially for cases that have an extensive dedifferentiated component and the uncertainty of the biological behavior of these tumors.