Objective: ADHD is a neurodevelopmental disorder affecting millions of adults worldwide. Continuous performance tests (CPTs) are widely used as assessment and diagnostic tools; however, their use in diagnosing undiagnosed ADHD in adults has been questioned due to their lack of specificity and sensitivity. This review sought to outline relevant findings concerning the diagnostic utility of the Conner’s Continuous Performance Test (CCPT) in adults. Method: This systematic review followed the a priori guide outlined by the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. Articles were gathered from PsycINFO, PsycArticles, Cochrane, Scopus, Google Scholar, and PubMed. Results: Thirty-five articles were reviewed and analyzed. Most articles reviewed used outpatient and university populations. Moderate reliability, subpar discriminant and ecological validity, and mixed sensitivity and specificity were noted. Conclusion: The results of this review lend support to previous critiques of the CCPT’s diagnostic and utility as a treatment measure.