Nonhuman primates (NHPs) naturally, spontaneously, and frequently develop a form of diabetes that is the same as Type 2 diabetes mellitus (T2DM) in humans.We have studied rhesus and cynomolgus monkeys prospectively longitudinally and have identified the natural history and phaselinked trajectory of multiple variables involved in the metabolic syndrome and prodrome to overt T2DM.We estimate that the lifetime prevalence of T2DM in rhesus (Macaca mulatta) approaches 30%, and under ad libitum feeding conditions of a healthy chow diet, more than 60% will be overweight or obese in middle-age.