In this study, we sought to evaluate a modification of the Michigan Alcohol Screening Test designed to include problems associated with other drug abuse/ dependence besides alcohol. Scores of the lifetime Michigan Assessment-Screening Test j Alcohol-Drug (MAST/AD) were compared to other lifetime measures of substance abuse and dependence and to psychiatric scales reflecting current or recent symptoms. Two university medical centers with alcohol-drug programs located within departments of psychiatry hosted 520 patients with alcohol-drug-related diagnoses. Patients completed their own MAST/AD using a paper-and-pencil format. Based on interviews with the patient, a research associate rated the patients’ substance-related problems on the Minnesota Substance Abuse Problem Scale (M-SAPS) and obtained information on lifetime treatment for substance abuse. An addictions psychiatrist determined abuse or dependence and made a current diagnosis of alcohol abuse/ dependence only, drug abuse/ dependence only, and alcohol plus drug abuse/ dependence. The MAST/AD was highly correlated with the M-SAPS and several other measures of substance abuse morbidity. Patients with alcohol-only and drug-only diagnoses did not differ from one another on the MAST AD, although both groups had lower scores than those with alcohol plus drug diagnoses. Current psychosocial morbidity as assessed by the patient and the psychiatrist was associated with the MAST/AD, although less strongly than with lifetime substance abuse measures. The lifetime MAST/AD demonstrates reliability as a severity measure for alcohol and/ or or drug abuse. With minor modification, this standard measure can be expanded from alcohol diagnoses to all substance diagnoses. This study in a clinical population did not demonstrate its utility as a screening instrument; additional work is needed to reveal its utility for this purpose. (Am J Addict 2004;13:151–162)