As a result of selecting triglycerides as the major vehicle for storing superfluous energy, evolution came up with a specialized cell type, the adipocyte, equipped to handle triglycerides and its potentially toxic metabolites--fatty acids. For the first time in history large human populations are subjected a wealth of cheap, accessible and palatable calories. This has created a situation, on a large scale not previously encountered, in which the capacity to store triglycerides in adipocytes is an important determinant of human health. Too few adipocytes (e.g. lipodystrophia) or a situation in which all adipocytes are filled, to their maximum capacity (e.g. severe obesity), will create very similar and unfavorable metabolic situations in which ectopic triglyceride stores will appear in tissues like liver and muscle. This review sets out to discuss the adipocyte and its role in metabolism as well as the consequences of a metabolic situation, in which the adipocyte has lost its fat storing monopoly.