Objective: Characterized by significant work-related impairments, difficulties with relationships, and higher rates of criminal behavior and substance abuse, ADHD is now understood as a disability that can persist throughout a lifetime. Differing opinions remain, however, regarding adult symptoms of ADHD, particularly with regard to gender differences. These issues add to the challenges of constructing a reliable and valid measure of ADHD for use with adults in research and practice. Method: We review the theoretical foundations of ADHD and psychometric properties of a major assessment device, the Conners’ Adult ADHD Rating Scales (CAARS). Results: Results of the literature review found (a) a wide range of internal consistency estimates, with lowest values for the Diagnostic and Statistical Manual of Mental Disorders (DSM)–Hyperactive/Impulsive Symptoms subscale when completed by women, and (b) discriminant validity estimates in the same range as convergent validity estimates. Conclusion: These findings raise questions about the construct validity of the CAARS and suggest directions for future research.