Appraisals of substance abuse often constitute a key component of psychological assessments affecting both diagnostic and treatment issues. Because of negative consequences, many substance users engage in outright denials and marked minimization regarding their drug use. Psychological measures, especially those with transparent items, are highly vulnerable to this denial. To address this response style, indirect items are often included on substance use measures to identify those who deny their use. The purpose of this study was to examine the effects of complete and partial denial on the Drug Abuse Screening Test–20, Substance Abuse Subtle Screening Inventory–3, and Drug Use Screening Inventory–Revised. Partial denial refers to the disacknowledgement of drug-related impairment interfering in multiple domains of a client’s functioning. The study used a mixed within- and between-subjects design with 102 inpatient substance users. Each participant completed the study under two conditions: a disclosing condition and an experimental condition (either complete denial or partial denial). Results show partial denial is distinctly different from complete denial across three self-report substance use measures. Importantly, substance users engaging in these denial conditions were often undetected by these measures. Contrary to expectations, subtle scales with indirect item content were only minimally more effective than the face valid scales alone for the assessment of denied drug use.