The amplification of MDM2 and CDK4 is the main molecular feature of well-differentiated liposarcomas (WDLS) and dedifferentiated liposarcomas (DDLS). Although the diagnostic usefulness of this molecular characteristic in liposarcomas has been investigated, its prognostic utility of quantitative gene level has not been explored. The aim of this study was to assess the prognostic significance of level of CDK4 amplification in MDM2-amplified WDLS/DDLS. MDM2 amplification in liposarcomas was confirmed by fluorescence in situ hybridization. The copy number of MDM2 and CDK4 was further determined by quantitative PCR (qPCR) and multiplex ligation-dependent probe amplification. Among 56 MDM2-amplified liposarcomas, 30 cases were assigned as WDLS, and 26 as DDLS. When liposarcomas were classified by qPCR-determined CDK4 amplification levels, the high-CDK4 group showed significantly poorer progression free survival (P=0.001) and disease specific survival (P=0.033) than the low-CDK4 group. However, MDM2 amplification level did not show prognostic significance. In WDLS/DDLS, the level of CDK4 amplification was useful for prognosis prediction and precise stratification of patients for targeted therapy.