The autonomic nervous system exerts a significant influence on body weight. This review underlines the role played by autonomic nervous system on food intake and energy expenditure, which are able to determine the body weight. An activation of the sympathetic discharges is usually associated with an increase in energy expenditure and a decrease in food intake, while reduction of food intake and body weight loss causes a reduction of the sympathetic activity. On the other hand, patho-physiological mechanisms of the obesity involve alterations of the sympathetic nervous system in accordance with the “Mona Lisa Hypothesis”, an acronym for “most obesities known are low in sympathetic activity”. Since the incidence of body weight superior to normal values is increasing in the industrialized word, the World Health Organization considers obesity as a pandemia in rich populations. Investigations on the vegetative control of control body weight give growing relevance to the possibilities of new strategies to reduce the incidences of overweight and obesity, which are frequently associated with metabolic and cardiovascular diseases