We report here on two cases of retroperitoneal liposarcoma which heterochronously occurred in two siblings. A huge myxoid liposarcoma, 20 x 14 cm size, was noticed in a 33-year-old female, who died with multiple liver metastasis in about half a year. Two years later after the death of the younger sister, pleomorphic liposarcoma, 8 x 8 cm in size, was noticed in a 39-year-old male who died with local recurrence and multiple metastasis one year after the operation. Their mother (69 years old) had had an operation for malignant fibrous histiocytoma of the right thigh at age 66. There was no evidence of multiple lipomatosis, an autosomal dominant trait, in the siblings or their family. Diverse soft-tissue sarcomas, but not liposarcoma, occur excessively in siblings with the syndrome of Li-Fraumeni. To our knowledge this is the first such report of its sibship occurrence.