Objective: To review the literature on the utility of the Conners CPT-3 in persons with ADHD. Methods: A systematic review was conducted. Six databases were searched using inclusion criteria: research studies, year 2000+, English, and ages 8+. Two raters independently screened 1,480 title/abstracts and subsequently reviewed 399 full texts. Data extraction and critical appraisal were conducted. Reflective thematic analysis through inductive coding identified qualitative themes. Results: Thirteen studies met inclusion criteria with five themes identified. Five studies found CPT-3 was a weak or poor predictor of ADHD diagnosis while two found it was an adequate predictor. Two studies found CPT-3 could differentiate clients with comorbid ADHD/anxiety from ADHD or ADHD from obsessive-compulsive disorder. One found CPT-3 could not differentiate ADHD from ASD or comorbid ADHD/ASD. Conclusions: Results revealed CPT-3 as a standalone measure is a weak or poor predictor of ADHD. Multiple measures for evaluating persons with ADHD are recommended.