This observational study estimates the extent to which alcohol disorder co-occurs in patients with major medical and psychiatric conditions. It looks at 2296 adult patients with hypertension, diabetes, heart disease (congestive heart failure or myocardial infarction) and/or current depressive disorder or subthreshold depressive symptoms, in the offices of general medical providers and mental health specialists in three U.S. cities. The authors compared the prevalence of alcohol co-morbidity in medically ill nondepressed patients of general medical providers and in depressed patients of both provider types. Results of the study show that patients with chronic medical problems or depression had similar levels of lifetime alcohol disorder (14 percent to 19 percent) and current alcohol problems (18 percent to 29 percent), but depressed patients were more likely to report needing help for problems with alcohol or drugs. Current alcohol disorder was more prevalent among depressed patients in mental health specialty practices than in general medical practices. Many patients who perceived a need for care for alcohol and other drug problems reported that this need was unmet (37 percent to 84 percent). The authors conclude that clinicians who treat patients with major medical and psychiatric conditions need to be prepared to identify and treat comorbid alcohol disorder.