Since low grade osteosarcoma may also harbour MDM2 amplification it is emphasised that the amplification has to be present in the lipomatous parts of the tumour to distinguish liposarcoma from extraosseous osteosarcoma.<h4>Conclusions</h4>The two cases exemplify challenges in the diagnoses of dedifferentiated liposarcoma. Here, MDM2 is linked to osteosarcoma.