Retinoid X receptors (RXRs) are involved in a number of signaling pathways as heterodimeric partners of numerous nuclear receptors. Hepatocytes express high levels of the RXRα isotype, as well as several of its putative heterodimeric partners. Germ-line disruption (knockout) of RXRα has been shown to be lethal in utero, thus precluding analysis of its function at later life stages. Hepatocyte-specific disruption of RXRα during liver organogenesis has recently revealed that the presence of hepatocytes is not mandatory for the mouse, at least under normal mouse facility conditions, even though a number of metabolic events are impaired [Wan, Y.-J., et al. (2000) Mol. Cell. Biol. 20, 4436–4444]. However, it is unknown whether RXRα plays a role in the control of hepatocyte proliferation and lifespan. Here, we report a detailed analysis of the liver of mice in which RXRα was selectively ablated in adult hepatocytes by using the tamoxifen-inducible chimeric Cre recombinase system. Our results show that the lifespan of adult hepatocytes lacking RXRα is shorter than that of their wild-type counterparts, whereas proliferative hepatocytes of regenerating liver exhibit an even shorter lifespan. These lifespan shortenings are accompanied by increased polyploidy and multinuclearity. We conclude that RXRα plays important cell-autonomous function(s) in the mechanism(s) involved in the lifespan of hepatocytes and liver regeneration.