Methods for assessment, e.g., anthropometric indicators and im- aging techniques, of several phenotypes of human obesity, with spe- cial reference to abdominal fat content, have been evaluated. The correlation of fat distribution with age, gender, total body fat, energy balance, adipose tissue lipoprotein lipase and lipolytic activity, adi- pose tissue receptors, and genetic characteristics are discussed. Sev- eral secreted or expressed factors in the adipocyte are evaluated in the context of fat tissue localization. The body fat distribution and the metabolic profile in nonobese and obese individuals is discussed rel- ative to lipolysis, antilypolysis and lipogenesis, insulin sensitivity, and glucose, lipid, and protein metabolism. Finally, the endocrine regulation of abdominal visceral fat in comparison with the adipose tissue localized in other areas is presented. (Endocrine Reviews 21: 697-738, 2000)