This article discusses the use of very-low-calorie diets (VLCDs) in the treatment of obese persons with non-insulin-dependent diabetes mellitus (NIDDM). Research using VLCDs with overweight participants with and without diabetes is reviewed. In both groups of participants, it has been shown that VLCDs used in combination with behavior therapy increase initial weight loss. However, to date, it has not been possible to develop treatment programs that maintain this weight loss long term. Neither intensive maintenance sessions nor intermittent VLCDs have been successful in maintaining the benefits of VLCDs long term. Thus, from the perspective of producing long-term weight loss, balanced low-calorie diets appear to be as effective as VLCDs. However, VLCDs may be useful in treating obese persons with NIDDM, because caloric restriction independent of notable weight loss has marked effects on glycemic control. Several studies have shown that just 7 days of caloric restriction can produce dramatic improvements in glycemic control; moreover, VLCDs produce greater improvements in glycemic control than more moderate diets, even if weight losses are the same. Research is needed to explore new ways to use VLCDs and other approaches to caloric restriction in the treatment of obese persons with NIDDM.