Physical training is useful as a therapeutic means to obtain a decrease in body fat. The success in terms of lost fat is dependent on the ability to adhere to the programme, and probably also on regulatory factors associated with the degree of filling of adipose tissue (adipocyte volume). The rate of weight loss is usually slower than with dietary treatment but physical exercise may be more successful and less uncomfortable in the long run as a means to lose weight and prevent regaining it. Physical training is also effective against the metabolic complications associated with obesity such as decreased glucose tolerance, hyperinsulinemia and hypertriglyceridemia and should therefore be a method of choice to prevent or treat adult onset diabetes mellitus and endogenous hypertriglyceridemia in obesity. The feasibility of training in different groups of subjects seems to be dependent on, among other factors, selection of subjects and design of the training programme.