Five cases of dedifferentiated liposarcoma in which heterologous elements were present in the dedifferentiated component are presented. Two patients, men 54 and 66 years of age, had retroperitoneal atypical lipomatous tumors (well-differentiated liposarcomas) that recurred (after 2.5 and 12 years, respectively) as dedifferentiated liposarcomas with rhabdomyosarcomatous elements in the dedifferentiated components. The third patient, a 63-year-old woman, had a retroperitoneal dedifferentiated liposarcoma whose dedifferentiated component demonstrated focal osteoid formation. The fourth patient, a 36-year-old woman, had two seemingly separate retroperitoneal masses, one composed of atypical lipomatous tumor with foci of smooth muscle and the other of leiomyosarcoma; despite the apparent separation, it was thought more logical to consider this a dedifferentiated liposarcoma with leiomyosarcoma as the dedifferentiated component than two unrelated neoplasms. The fifth patient, a 45-year-old man, had a mediastinal dedifferentiated liposarcoma with angiosarcomatous areas in the dedifferentiated component. The relatively short follow-up thus far available on these cases has not demonstrated tumor behavior significantly different from that of dedifferentiated liposarcoma as a whole.