Objective: This study measured the effects of atomoxetine HCI on high-risk behaviors and health-related quality of life in adolescents with attention-deficit/hyperactivity disorder (ADHD), using a subgroup analysis of data from a previous clinical trial. Research design and methods: In the base study, which was conducted at 26 sites in the United States, patients ages 13-16 years were randomized in a double-blind manner to atomoxetine treatment by one of two dose titration schedules for 8 weeks. Patients who responded to treatment were rerandomized to atomoxetine at a daily dose of 0.8 or 1.4 mg/kg for 40 weeks. Patients in the highest-risk quartile for each category of behavior or domain were included and the dosing groups combined. Main outcome measures: Efficacy measures included the Youth Risk Behavior Surveillance (YRBS) and Child Health and Illness Profile - Adolescent Edition (CHIP-AE). The YRBS has six categories of behavior, and the CHIP-AE has six domains. Data for mean change from baseline were analyzed using a last-observation-carried-forward analysis. Results: A total of 267 patients were randomized, but the high-risk subgroup analyzed in the present study was much smaller (range of n = 5-68 per group). YRBS scores for tobacco use, unhealthful dietary behaviors, inadequate physical activity, and behaviors contributing to unintentional injuries showed statistically significant improvements (p < 50.05) by atomoxetine treatment at Week 8. At the end of the 40-week maintenance period, unhealthful dietary behaviors, inadequate physical activity, and behaviors contributing to unintentional injuries continued to show statistically significant improvements (p < 0.001). When the highest-risk quartile of the CHIP-AE data was analyzed, there were statistically significant improvements on all six domains after atomoxetine treatment at 8 weeks (p < 0.001) and on five of the six domains at 40 weeks (p <= 0.01). Conclusions: Atomoxetine improved self-reported high-risk behaviors and overall health-related quality of life in adolescents with ADHD. Potential limitations of this study include small sample sizes and the fact that it involved a subgroup analysis, which is by nature hypothesis-generating. Further, well-controlled, prospective studies in larger and more heterogeneous ADHD populations, including older patients, are warranted to confirm or reject these findings.