In the normal population, the prevalence of obesity is almost 20%. It is a condition influenced by genetic factors, so that individual behavior cannot be regarded as its sole cause. The amount of food is essentially determined by the hormone leptin, the feedback regulation of which can be disturbed by a modification of the molecule or a mutation of the receptor. A further important determinant is energy consumption, which is subject to large individual variations, which partly result from thermogenesis. With regard to the fat distribution, it is concentrated on the trunk in the android form as compared to the hips in the gynecoid form. The android form is subject to a higher incidence of cardiovascular morbidity and mortality. The indirect determination of body fat by measuring the body mass index (weight [kg]/body weight [m(2)]) is hence less reliable than measuring the waist (women > 80 cm, men > 94 cm). The effects of generalized obesity on cardiovascular function are chiefly an increase of blood volume and an eccentric left ventricular hypertrophy. This first of all results in diastolic dysfunction, which can give rise to a disturbance of systolic function in left ventricular dilatation. Concentric hypertrophy develops in the presence of arterial hypertension. This is twice as frequent in obese patients than in the normal population, which is due to increased activity of the sympathetic nervous system and stimulation of the renin-angiotensin system. A disturbance of lipid metabolism is observed four to six times more frequently. The qualitative change in LDL fraction with a raised concentration of low density LDL particles appears to be of crucial importance. With increasing fat mass, the sensitivity to insulin is lowered, so that in obesity the risk of developing diabetes mellitus type 2 is tripled. Since there has been a dramatic increase in the numbers of overweight children and adolescents (from 10.5% to 15.5% within the past five years), prevention programs should be started in good time. A reduction in calorie intake and an altered dietary composition (55% complex carbohydrates, 30% fat and 15% to 20% protein) on the one hand, and increased physical activity on the other hand continue to be the central components. The latter is especially effective when it regularly gives rise to an increased turnover of fatty acids as a result of an increased energy metabolism at moderate intensity. This leads to adaptation, i. e. an increase in the activity of lipoprotein lipase. If prevention programs and/or changes in lifestyle do not give rise to the desired weight reduction, medication is indicated in some adults. Sibutramine (Reductil and orlistate (Xenical) lead to an additional weight loss of up to 10%. However, consistent treatment of any cardiovascular risk factors present is more important. Treatment of arterial hypertension is of greatest prognostic significance, especially in concomitant diabetes mellitus. In individual cases and after thorough discussion of indication surgical options should be considered.