ABSTRACT We examined the effects of atomoxetine in Latino (n = 108) versus Caucasian (n = 1090) pediatric outpatients (aged 6 to <18 years) during the first 10-11 weeks of treatment in two multicenter, open-label trials. Mean modal doses were not significantly different in Latinos (1.22 mg/kg per day) versus Caucasians (1.27 mg/kg per day; p = 0.22). Both groups showed significant and similar improvements: Mean ADHD Rating Scale-IV-Parent Version: Investigator Administered and Scored (ADHDRS-IV-P:I) scores decreased by 54% in Latinos (40.9-18.9; p < 0.001) and by 52% in Caucasians (37.7-18.2; p < 0.001). Other efficacy measures, such as Conners' Parent Rating Scale-Revised: Short Form (CPRS-R:S) and Clinical Global Impressions-ADHD-Severity (CGI-ADHD-S), demonstrated similar and significant decreases. The only significant between-group difference was a greater decrease in the ADHDRS-IV-P:I Hyperactive/Impulsive subscale at weeks 8-11 for Latinos; however, Latinos had higher baseline scores compared with Caucasians. This was not demonstrated in the CPRS-R:S Hyperactivity subscale. There was a significantly higher frequency of CYP2D6 slow metabolizers in Caucasians compared with Latinos. Caucasians reported significantly more abdominal and throat pain, whereas Latinos reported more decreased appetite and dizziness, but no differences in other common adverse events were reported. No suicidal behavior was reported in either group. We found that Latino and Caucasian children with attention-deficit/hyperactivity disorder (ADHD) exhibit a similar pattern of efficacy and tolerability with atomoxetine. The lack of placebo controls was a limitation of this study.