The peroxisome proliferator-activated receptor-gamma (PPARgamma, NR1C3) in complex with the retinoid X receptor (RXR) plays a central role in white adipose tissue (WAT) differentiation and function, regulating the expression of key WAT proteins. In this report we show that poly(ADP-ribose) polymerase-2 (PARP-2), also known as an enzyme participating in the surveillance of the genome integrity, is a member of the PPARgamma/RXR transcription machinery. PARP-2(-/-) mice accumulate less WAT, characterized by smaller adipocytes. In the WAT of PARP-2(-/-) mice the expression of a number of PPARgamma target genes is reduced despite the fact that PPARgamma1 and -gamma2 are expressed at normal levels. Consistent with this, PARP-2(-/-) mouse embryonic fibroblasts fail to differentiate to adipocytes. In transient transfection assays, PARP-2 small interference RNA decreases basal activity and ligand-dependent activation of PPARgamma, whereas PARP-2 overexpression enhances the basal activity of PPARgamma, although it does not change the maximal ligand-dependent activation. In addition, we show a DNA-dependent interaction of PARP-2 and PPARgamma/RXR heterodimer by chromatin immunoprecipitation. In combination, our results suggest that PARP-2 is a novel cofactor of PPARgamma activity.