The extremely high prevalence of obesity makes it a social health problem in this century. The fact that this prevalence has increased over the last 50 years is of great importance. Moreover, increased mortality is the major negative consequence of obesity, and the risk of death grows accordingly to BMI increase. The paper presents epidemiological data on overweight and obesity, and their clinical sequelae. Also, the role of fat tissue in the pathogenesis of obesity is discussed in the article.