Objective: When adults are evaluated for ADHD, the Conners' Adult ADHD Rating Scale (CAARS) and Conners' Continuous Performance Test, Second Edition (CCPT-2) are frequently used in conjunction with an omnibus measure of personality such as the Personality Assessment Inventory (PAI). The purpose of this study was to determine the concurrent validity among these three measures. Method: This is a retrospective study of 72 cases from a University-based clinic database. Adults (M = 22.42, SD = 7.28) were self-referred for a comprehensive evaluation. The sample included 40 males and 32 females and was predominantly White non-Hispanic (58%). Diagnoses included ADHD, Learning Disorder, Anxiety, or Depressive Disorder. Data was analyzed using SPSS 22.0 to determine the concurrent validity between the measures. The five subscales for the CAARS-Short Form and five variables from the CCPT-2 were examined in relation to the PAI subscales. Results: Five subscales on the CAARS-Short Form correlated moderately with the PAI subscales Anxiety (r = .30−.54, p < .01), Borderline (r = .30−.66, p < .01), and Schizophrenia (r = .30−.54, p < .01). Depression correlated with all CAARS subscales except for Hyperactivity/Restlessness (r = .34−.56, p < .01). None of the five variables of the CCPT-2 were correlated with subscales of the PAI. Conclusion(s): Adults exhibiting symptoms of ADHD usually experience global difficulties that appear to be better assessed by the PAI and the CAARS. Therefore, the PAI can be a useful measure to assist with treatment planning for adults exhibiting symptoms of ADHD as well as co-morbid symptoms related to other clinical disorders.