The relation between mind and body has been keen of interest since antiquity. The author surveys the approaches to the subject from the observational to the experimental level. He presents the findings of a study carried out, at a community health screening survey, to test the association between physical and psychiatric disorder. The methodological difficulties of this kind of study, such as sampling the general population and reliable measurement of clinical states, are described. The results of the study, which confirm the two types of morbidity have a positive and significant association, are discussed in terms of the ecology of disease and psychosomatic medicine. It is suggested that the findings have implications for the delivery of health care and preventive medicine.