Chronic disease management (CDM) is a collaborative, longitudinal, proven effective approach to the treatment of chronic medical illnesses that addresses individual patient and health systems barriers to receipt of needed treatment. The objective of this Addiction Health Evaluation And Disease management (AHEAD) Study is to test the effectiveness of CDM for substance dependence in primary care. The study will enroll and randomize subjects to attend a substance dependence CDM program (the AHEAD Unit) integrated into a real-world primary care clinic or to referral to usual primary care. All subjects will be assessed regarding alcohol and/or drug diagnosis, consumption and problems, readiness to change, health-related quality of life, and medical and substance abuse treatment utilization. Primary outcomes are alcohol and drug use, alcohol and drug-related problems, emergency department visits, and hospitalizations. Additional outcomes are health-related quality of life, readiness to change, medical and psychiatric comorbidity, HIV risk behaviors, and treatment utilization and costs. The hypothesis is that compared with standard care, a health services intervention -- chronic disease management for alcohol and drug dependence integrated in primary care -- will decrease alcohol and drug use and related problems, and improve health care utilization patterns.