The adipose tissue stores excess energy but also produces a series of substances including cytokines (adipocytokines) which participate in regulatory processes. The physiologic and pathophysiologic relevance of these factors has only recently been described in more detail. Defects in adiponectin as well as overproduction of free fatty acids play an important role in the development of insulin resistance typical for obesity. Rare forms of obesity or lipodystrophy can now be explained by defects in the leptin system. The contribution of adipose tissue and its cytokines to the relationship between inflammation and the metabolic syndrome is currently under investigation.