Several publications have described biological roles for human patatin-like phospholipases (PNPLAs) in the regulation of adipocyte differentiation. Here, we report on the characterization and expression profiling of 10 human PNPLAs. A variety of bioinformatics approaches were used to identify and characterize all PNPLAs encoded by the human genome. The genes described represent a divergent family, most with a highly conserved ortholog in several mammalian species. In silico characterization predicts that two of the genes function as integral membrane proteins and are regulated by cAMP/cGMP. A structurally guided protein alignment of the patatin-like domain identifies a number of conserved residues in all family members. Quantitative PCR was used to determine the expression profile of each family member. Affymetrix-based profiling of a human preadipocyte cell line identified several members that are differentially regulated during cell differentiation. Cumulative data suggest that patatin-like genes normally expressed at very low levels are induced in response to environmental signals. Given the observed conservation of the patatin fold and lipase motif in all human PNPLAs, a single nomenclature to describe the PNPLA family is proposed.