Millions of Americans suffer and die of alcohol abuse, other drug abuse, and mental disorders that go undiagnosed and untreated. Studies showing that up to 19% of the US adult population have these disorders also have found that only one fifth of those affected have sought help for them in the previous six months. Many of these persons have disorders that are treatable with modern medications and therapy. Because more than half of all persons with these disorders obtain all of their care from the general medical sector, a great potential exists in primary care for prevention, detection, treatment, and referral of these patients. Primary care physicians, however, have not been very successful at diagnosing and treating substance abuse and mental disorders because of inadequate training, patients' attitudes, and the constraints of the health care system. Recommendations to improve this situation include continued research, improved physician education, and increased emphasis on care of these disorders by organized medicine. Although tobacco use is also a major health problem, data relating to nicotine addiction were not included in this report.