Obesity is known as an independent risk factor of a number of chronic noninfectious disorders, however some investigations testify to the presence of "obesity paradox". The aim of the present review was to analyze results of investigations purposed to assess the effect of an elevated body mass index (BMI) and obesity on hospital mortality, risk of complications, and long term prognosis (mortality rate). Effect of BMI dynamics during lifespan on (cardiovascular ?) mortality was also analyzed. The results failed to demonstrate any convincing evidences that BMI 25-35 kg/m2 alone without taking into consideration metabolic changes, waist measurements, correlation between fat and muscular tissue was a risk factor of higher mortality in the long-term prospect and that its decrease improved survival. At the same time, it should be noted that these results depended on the method of sample formation and approaches to the statistical analysis.