Akin to humans, lipomas are common in the dog as well; however, until now there were no reports of cytogenetic investigations on these tumors in the canine. We report our results of cytogenetic investigations on a series of ten canine lipomas. Clonal aberrations were observed in seven cases. In one case a trisomy 27 was evident; in another case a trisomy 13 was present in addition to a marker chromosome. A third lipoma showed a fusion of chromosomes 2 and 13. These cases showed one derivative chromosome each (der(X), der(7), and der(4)), and one case had two derivative chromosomes (der(X) plus der(4)). In the two cases with derivative chromosomes 4, the same region (4q31) was affected. It is tempting to speculate that this region might harbor a gene associated with tumor development. The results are compared to the cytogenetic situation in human lipomas.