Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors, initially described as molecular targets for synthetic compounds inducing peroxisome proliferation. PPAR-gamma, the best characterized of the PPARs, plays a crucial role in adipogenesis and insulin sensitization. Furthermore, PPAR-gamma has been reported to affect cell proliferation/differentiation pathways in various malignancies. We discuss in the present review recent advances in the understanding of the function of PPAR-gamma in both cell proliferation and adipocyte differentiation.