Non-insulin-dependent diabetes mellitus afflicts ten million Americans (half of whom are undiagnosed) and often is diagnosed only because of its complications. When diagnosed, it is generally treated inadequately. The key to appropriate management is an evaluation of each patient's pathophysiology by careful physical and laboratory examinations. A clear understanding of the therapeutic actions of diet, exercise, sulfonylurea agents, and the new insulins permits the physician to design a specific treatment regimen that can restore normal or near-normal glycemic and lipid control, overcome insulin resistance, and prevent, delay, or slow the course of complications that result from the toxic effects of hyperglycemia.