A patient with Werner's syndrome, partial lipoatrophy and diabetes mellitus presented several of the metabolic alterations found in obesity and maturity-onset diabetes, in spite of a total body-fat mass which was markedly reduced when compared to randomly-selected women. The data show elevated blood sugar and free fatty acids, hyperinsulinemia, elevated glucaon and suppressed growth-hormone levels. Metabolic studies with isolated adipocytes show evidence of increased lipolytic response to catecholamines, diminished binding of insulin and decreased antilipolytic effect of this hormone. A striking feature of this patient's adipose tissue was the contrast between lipoatrophy in the subcutaneous tissue of the extremities and augmented abdominatl subcutaneous adipose tissue. The adipocyte size in this region was very large (1.6 micrograms lipid/cell) and among the largest ever recorded in this laboratory. It is proposed that a'regional adiposity', particularly in the abdominal area, with enhanced adipocyte size and adipocyte metabolic contributions, may promote the metabolic events and alterations that are more typically observed in the generalized form of obesity.