Glucagon-like peptide-1 (GLP-1) is an incretin hormone capable of restoring euglycemia in glucose-intolerant subjects and improving glucose control in individuals with type 2 diabetes. Whether the antidiabetic properties of GLP-1 are exclusively the result of its acute postprandial action is being investigated. A GLP-1-dependent differentiation of pancreatic precursor cells into mature β-cells has been proposed. In addition, GLP-1 has been shown to have antiapoptotic activity in cultured insulin-secreting cells and in an animal model in which diabetes occurs as a consequence of an excessive rate of β-cell apoptosis. Studies from our laboratory, and others, lead us to propose that GLP-1 is a growth factor for pancreatic cells and it is a regulator of islet cell mass. 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 as well as its insulin secretory action.