This chapter deals with a description of some of the general themes that are pertinent across all disorders in their presentation within general hospitals. Mental health services in general hospitals see only a tiny minority of all those with psychiatric disorders. Depression and anxiety are common in general hospital patients, and there is a strong epidemiological association between physical disease and common mental disorders in the wider population. Few studies have described the natural history of depression and anxiety in medically ill patients. There is a close association between psychiatric disorders and unexplained symptoms. Many patients with unexplained symptoms are prescribed antidepressants. A common reason for referral to liaison psychiatrists is to determine whether a patient has mental capacity or competence to make a treatment decision. Such patients tend to be older, have more cognitive impairment and neurological disorders than patients who have mental capacity.