OBJECTIVES: Childhood attention-deficit/hyperactivity disorder (ADHD) frequently persists into adulthood and continues to impair health-related quality of life (HRQL). The 29-item, patient-report Adult Attention-Deficit/Hyperactivity Disorder Quality of Life Scale (AAQoL) was developed to assess HRQL among adults with ADHD. In the initial validation study with a sample drawn from a managed health care plan, the measure demonstrated good psychometric properties. The purpose of the current analysis was to further evaluate the AAQoL in a clinical trial sample. METHODS: Data were from baseline and week 8 of a randomized, placebo-controlled trial of atomoxetine among adults with ADHD. Patients completed the AAQoL, Adult ADHD Self-Report Scale (ASRS), Conners' Adult ADHD Rating Scale (CAARS), SF-36, and Endicott Work Productivity Scale (EWPS). Clinicians completed a global measure of severity (CGI-ADHD-S). Internal consistency reliability (Cronbach's alpha) and construct validity (correlations, ANOVAs) of the AAQoL were examined. RESULTS: The 410 enrolled patients were 58.5% male with a mean age of 36.8 years. There were no substantial floor effects, ceiling effects, or missing data for any AAQoL items. At baseline, Cronbach's alpha was 0.89 for the total score and 0.76 to 0.82 for the subscales. AAQoL baseline scores were significantly correlated with the EWPS (r = -0.36 to -0.61; all p <0.001), all ASRS scales (r = -0.10 to -0.62; all p <0.05), most SF-36 scales (r = 0.03 to 0.68) and most CAARS scales (r = -0.05 to -0.57). AAQoL scores significantly discriminated among patients with different levels of clinician-rated (CGI-ADHD-S) and patient-reported (CAARS) symptom severity at baseline. All results followed similar patterns at week 8. CONCLUSION: The AAQoL demonstrated good reliability and validity in this clinical sample. Results add to previous research suggesting that the AAQoL is a useful measure of HRQL among adults with ADHD.