The application of epidemiology to the study of non-insulin-dependent diabetes mellitus (NIDDM) is providing new insights into many aspects of this major public-health problem, including its natural history, prevalence, incidence, morbidity, and mortality in diverse populations around the globe. The main impetus came from the late Kelly West's book Epidemiology of Diabetes and its Vascular Lesions. These studies are providing direction for research into the possible moleculardefect or defects and biochemical mechanism or mechanisms underlying NIDDM and important information on the extrinsic (social, cultural, environmental) risk determinants. Studies have highlighted the importance of regional adipose tissue distribution, particularly upper-body obesity, and physical inactivity in enhancing risk of NIDDM. These findings have important implications for the primary prevention of NIDDM, particularly in populations with increased genetic susceptibility such as Polynesians, Micronesians, American and Asian Indians, Mexican Americans, and Australian aborigines.