Factors potentially associated with adult-onset diabetes mellitus in the elderly were reviewed, using the Framingham Heart Study data and other population data. Incidence data for diabetes mellitus in the elderly are sparse, but they indicate that the prevalence of diabetes increases greatly with age. Prevalence rates commonly exceeded 10 percent in those over the age of 60. Men and women in the Framingham Study who were overweight by more than 40 percent had twice the prevalence of diabetes mellitus compared with those of normal weight. Hypertension and coexistent vascular disease were particularly common in elderly diabetic patients, with rates markedly greater than those found among younger adult-onset diabetic patients. In those 50 years of age or older, the later development of diabetes mellitus was associated with increased levels of very-low-density lipoprotein cholesterol, decreased levels of high-density lipoprotein cholesterol, obesity, elevated casual glucose levels, use of diuretics, and preexisting vascular disease.