Glucagon-like peptide-1 (GLP-1), a peptide hormone produce by intestinal cells, has recently been shown to be capable of modulating islet cell mass. Administration of GLP-1 to rodent models of type 2 diabetes ameliorates insulin secretion, induces the replication of islet cells, and promotes islet-cell neogenesis from pancreatic ductal cells susceptible to transdifferentiate in insulin-producing cells. In addition, an anti-apoptotic effect of GLP-1 has been described in hyperglycemic animal models, using freshly isolated human islets or cultured beta cell lines exposed to various pro-apoptotic stimuli. The aim of this article is to review those reports that have emphasized the role of GLP-1 as a regulator of islet cell mass.