A survey of opinions on the causes and effectiveness of treatment of obesity was carried out on 50 physicians and scientists involved in obesity research. Responses were grouped by region (Europe, North America, and United Kingdom), sex, age (30-50 and greater than 50 y) and degree (MD or PhD). Genetic factors were considered the most important causes of obesity overall. Females viewed lack of physical activity, carbohydrate craving, and weight cycling as significantly more important causes than did their male colleagues and viewed exercise as a more effective treatment. There were regional variations in the assessment of the importance of metabolic defects and weight cycling as causes of obesity and in the usefulness of diet in the treatment of obesity. The older group of respondents rated low-fat diet more highly as a treatment than did their younger colleagues. All groups viewed serotonergic and thermogenic drugs as effective treatments whose usefulness would increase during the next 10 years.