The Barkley Adult ADHD Rating Scale-IV (BAARS-IV) and Clinical Assessment of Attention Deficit-Adult (CAT-A) are self-report measures of attention-deficit/hyperactivity disorder (ADHD) symptoms. Yet, no study to date has examined these measures concurrently in a clinical sample. This study sought to investigate the relationship between the CAT-A and BAARS-IV in a sample of adults referred for an ADHD evaluation. This cross-sectional study examined data from 142 adults in the United States (62% Female; 40% Non-Hispanic White) referred for neuropsychological evaluation for ADHD diagnostic clarification. Participants completed the CAT-A and BAARS-IV and a neurocognitive battery. Participants were divided into ADHD-only (n = 54), ADHD + Internalizing (n = 54), and Internalizing Disorder-only (n = 34) groups based on their diagnosis following the evaluation. The ADHD + Internalizing Disorder group had the highest rates of elevations on the CAT-A and BAARS-IV scales assessing childhood symptoms and had the highest rates of elevations for total current symptoms across both measures compared to the Internalizing Disorder group. Rates of concordance for the CAT-A and BAARS-IV within the full sample (73-80%) and across diagnostic groups (69 − 91%) were high. When cases were discordant, participants were more likely to have clinically elevated BAARS-IV scores and non-elevated CAT-A scores. Although the BAARS-IV and CAT-A are largely concordant measures, the high rate (i.e., > 50%) of current symptom endorsement across diagnostic groups suggests these measures are not exclusively sensitive to ADHD and therefore should not be used as sole indicators of ADHD.