This paper describes an assessment of expert medical and epidemiological opinion about the role of lifestyle in health, carried out by means of a questionnaire survey of senior members of academic departments of public health, epidemiology and social medicine in Western European universities. Estimates were made of the influence of eight lifestyle factors--smoking, alcohol consumption, exercise, stress, body weight, dietary fat, fibre and salt--on the aetiology or course of five disorders: heart disease, high blood pressure, lung cancer, breast cancer and diabetes. One hundred and fifty responses were received from scientists and clinicians from 16 countries. Respondents had an average of 17.8 years experience in their discipline (range 5-40 years). The only links to be endorsed as definite by over 90% of respondents were those between smoking and both heart disease and lung cancer. However, more than 70% considered alcohol consumption, exercise, stress body weight and dietary fat to be definite or probable influences on heart disease. Smoking, alcohol, exercise, stress, body weight and salt intake were endorsed as relevant to high blood pressure by more than 70%. Opinions differed widely about the influence of lifestyle on breast cancer and diabetes. Experts from the United Kingdom and Republic of Ireland were less positive than respondents from other countries about the influence of stress, dietary fat, fibre and salt on disease. The results indicate that comparatively few lifestyle factors were believed to be unequivocally related to any of the five disorders. Experts from the UK and Ireland were generally les likely to endorse lifestyle-disease links than those from other European countries.(ABSTRACT TRUNCATED AT 250 WORDS)