Cytogenetic analysis of a short-term culture from a round cell liposarcoma revealed ins(12;16)(q13;p11.2p13) as a sole abnormality in all metaphase cells studied. This chromosome rearrangement, thus far not described in liposarcomas, leads to recombination of bands 12q13 and 16p11.2 and, thus, seems to be the equivalent of t(12;16)(q13;p11), a translocation that is highly specific for the myxoid type of liposarcoma. Our case represents the fourth fully karyotyped round cell liposarcoma that displays a cytogenetic rearrangement of bands 12q13 and 16p11, thus supporting the concept that round cell liposarcoma is related to myxoid liposarcoma and constitutes its poorly differentiated form. The fact that ins(12;16) was the only detectable chromosome aberration suggests that the presence of secondary cytogenetic aberrations is not a prerequisite for the development of a round cell histology in liposarcoma.