We assessed the reliability of the Medical Outcomes Study Short Form Health Survey (SF-20) in a heterogeneous group of persons seeking drug and alcohol treatment. Patients (n = 2688) seeking detoxification and treatment at four intake sites for Addiction Treatment in Boston, Massachusetts, received all components of the SF-20 including physical, role, and social functioning; mental health; health perception and bodily pain. The primary drugs used were alcohol 38%, cocaine 38%, heroin 24%. Reliability coefficients for the MOS scales ranged from 0.70 to 0.92. Users of these three drugs had similar profiles among the health components. Sociodemographic characteristics in combination explained 2-7% of score variance. Alcohol and other drug use had little effect on physical or role function scores. Health perception and pain subscale scores were low. We conclude the MOS survey is a reliable measure of function and well being in this population. Like other chronic diseases, alcohol and drug use have powerful effects on quality of life.