Objective: When assessing adult ADHD, it is best practice to use several measures for clinical diagnosis. The authors hypothesized that different subtests measuring underlying constructs of ADHD symptomology on the Conners' Adult ADHD Rating Scale (CAARS), Behavior Assessment System for Children-College 2nd Edition (BASC-2), and the Conners' Continuous Performance Test-II (CCPT-II) would be statistically correlated. Method: Data were collected retrospectively from a local university counseling and assessment-training clinic. A total of 193 participants (114 male and 81 female) completed the CAARS and BASC-College self-report forms, as well as the CCPT-II. Participant age ranged from 18 to 36 (M = 20.31; SD = 2.92). Of the participants included, 181 were diagnosed with a Learning Disability, ADHD, Anxiety, Depression, or a combination. Results: Analyses included Pearson r correlations, which revealed statistical significance for several subtests. The Inattention/Memory Problems on the CAARS was statistically significant (p < .001) with Attentional Problems and Inattention/Hyperactivity Clinical subscales on the BASC-College. The Impulsivity/Emotional Lability subscale (CAARS) was statistically significant (p < .001) with Atypicality and Locus of Control (BASC-College). No statistical significance was found between the CCPT-II and other measures. Full correlation matrix and additional findings will be provided. Conclusion(s): Findings from this study demonstrate acceptable rates of convergent validity between the CAARS and BASC-College. Our results support the clinical utility of these two measures when diagnosing adult ADHD. Consistent with previous research, the CCPT-II was not statistically correlated with the behavior rating scales. Consequently, laboratory assessments may not be a valid measure of ADHD symptomology across settings.