Purpose: To determine knowledge of a national sample of medical students about substance withdrawal, screening and early intervention, medical and psychiatric complications of addiction, and treatment options. Methods: Based on learning objectives developed by medical faculty, twenty-two questions on addictions were included in the 1998 Canadian licensing examination. Results: The exam was written by 858 medical students. The average score on the addiction questions was 64%. Students showed strong knowledge of the clinical features of medical complications. Specific knowledge gaps were identified for withdrawal treatment protocols, low-risk drinking guidelines, taking an alcohol history, substance-induced psychiatric disorders, and Alcoholics Anonymous. Conclusion: Medical students are knowledge-deficient around key learning objectives in addictions. The deficiencies were in areas of basic knowledge that could be learnt with little difficulty. (Contains 3 tables.)