The prevalence and incidence of overweight and obesity has been studied in a young adult population aged 19-35 years. Special attention was given to the relation with psychosociological variables and life-style. The prevalence of overweight and obesity was also studied in a representative population for The Netherlands, in which population also the relation with self-reported illness and subjective health was studied. In the patient population of four general practices the relation of overweight and obesity with disease was investigated in a retrospective design. Also the influence of the body fat distribution was studied. The prevalence of overweight (BMI greater than 25 kg/m2) in the Dutch adult population was 34% in men and 24% in women. The prevalence of obesity (BMI greater than 30 kg/m2) was 4 and 6% in men and women, respectively. The prevalence of overweight and obesity was negatively related with social class and increased with age. Also, life-style variables such as coffee consumption, alcohol consumption, smoking and amount of hours sleep (CASS behavior), physical activity during leisure time, slimming behavior and health-conscious behavior were correlated with the prevalence of overweight. Life events caused an increase in body weight, but in women (not in men) this gain was suppressed by following slimming periods. Thus, emotional eating seems to be an important factor in the etiology of obesity. The results of our studies on the relation of overweight and obesity with morbidity aspects show a clear relation of some diseases and subjective health with overweight, especially in men and women with an abdominal fat distribution. From the results of this study starting points for the prevention and treatment of obesity are proposed.