According the Substance Abuse and Mental Health Services Administration (2013), an estimated 23.9 million Americans are current illicit drug users. These numbers raise serious concerns given the devastating consequences of addiction borne by individuals, families, communities and society as a whole. Furthermore, The National Institute on Drug Abuse (2012) estimates that addiction costs the nation in excess of $600 billion annually. Given this, it is important to evaluate instruments and measures utilized by treatment professionals to assess and diagnose substance use disorders. The purpose of this paper shall be to undertake such an evaluation of two widely used assessment protocols – the Substance Abuse Subtle Screening Inventory (SASSI) and the Addiction Severity Index (ASI) – by appraising the reliability, validity, feasibility, accessibility, and overall appropriateness of these measures in screening and assessing adults with substance use disorders.