This article reviews recent epidemiological findings on the relationship between physical and psychiatric conditions. First, physical disorders may be a risk factor of mental disorders. The WHO World Mental Health (WMH) Surveys indicated that the prevalence of most mental disorders were high among persons with a variety of physical disorders. Second, mental disorders may affect the course and prognosis of physical disorders. Several studies reported increased mortality when depression was comorbid with cancer, stroke, heart disease and diabetes. Third, social functioning was more deteriorated among those with comorbid physical and mental disorders than those with either of them. The comorbidity with mental disorders and its impact on the longevity and social life are observed for most physical disorders.