Substance use disorder is a significant problem in the United States causing considerable distress and cost to the healthcare system as well as familial, community, and societal resources. Based on evidence-based research, a statement by the United States Preventive Services Task Force in 2015, recommends substance use disorder screening for adults in the primary care setting. A review of the literature concerning screening tools for substance use disorder resulted in twelve studies being included. The purpose of this project is to determine if the more comprehensive substance use disorder screening tool, ASSIST, identifies more at risk patients than the current CAGE-AID screening tool in order to improve early identification and intervention. The ASSIST questionnaire consists of 8 questions that investigate past and current use of substances. Developed by the World Health Organization (WHO), it has been shown to be reliable and valid. Patients 21-55 years from one primary care clinic in NJ were asked to voluntarily participate in a substance use disorder screening using the ASSIST screening tool. This tool was administered at well and follow up visits. The results were compared to the results of the CAGE-AID screening tool which is already part of the intake. Results showed that of the 36 people interviewed, ASSIST (n=14, 38.8%) identified more people at moderate or high risk compared to CAGE-AID (n=1, 2.7%). While this was a small study, more investigation is warranted as the results suggest that a more comprehensive screening tool is identifying those at risk more often especially for those in the medium risk category. Those patients in need of intervention are more likely to be identified with ASSIST and intervention can be begun as early as possible. Keywords: primary care, screening tools, substance use disorder