Well-differentiated liposarcomas (WDL) are intermediate malignant, locally aggressive mesenchymal neoplasms. The cytogenetic hallmarks of WDL are supernumerary rings and giant marker chromosomes containing material mainly from chromosome arms 1q and especially 12q, but also occasionally from other chromosomes. WDL are typical examples of tumors that may become more aggressive with time. One would assume that additional genomic changes lie behind the acquisition of such a more dangerous phenotype, and yet very little is known about the putative, late-occurring genomic aberrations in recurrent WDL. We have undertaken a pairwise comparison of the genomic imbalances occurring in primary and recurrent WDL from the same patient. In one of the cases, the patient's final recurrence, which was 17 years after the primary tumor and showed more pronounced nuclear atypia, had seven additional genomic changes compared with what was found in the primary tumor. The findings illustrate that the phenotypic changes some WDL undergo with time may have a genomic correlate, and that a pathogenetic continuum exists between WDL and dedifferentiated, more malignant liposarcomas.