To assess efficacy and safety of the new Dextroamphetamine Transdermal System (d-ATS) to treat children and adolescents (aged 6-17 years) with attention-deficit/hyperactivity disorder (ADHD). In this phase 2, randomized, placebo-controlled study, 4 d-ATS patches of differing doses (5, 10, 15, and 20 mg) were evaluated. Patients began a 5-week, open-label, stepwise dose-optimization period in which they received a 5-mg d-ATS patch (applied to hip) for 9 hours. During weekly visits, patients were evaluated for possible adjustments to the next dose level based on efficacy and safety. Once at the optimal dose, that dose was maintained during a 2-week, crossover double-blind treatment period. Primary endpoint was to assess efficacy of d-ATS versus placebo as measured by Swanson, Kotkin, Agler, M-Flynn, and Pelham Scale (SKAMP) total score; key secondary endpoints included assessing onset and duration of efficacy by SKAMP total score, and additional secondary endpoints included Permanent Product Measure of Performance (PERMP) scores. Safety was assessed throughout. d-ATS treatment resulted in significant improvements versus placebo in ADHD symptoms as measured by SKAMP total score, with overall least-squares mean difference (95% confidence interval) versus placebo of -5.87 (6.76, -4.97;  < 0.001) over the 12-hour assessment period. Onset of efficacy was observed at 2 hours postdose ( < 0.001), and duration of effect continued through 12 hours (patch removed at 9 hours), with significant differences between d-ATS and placebo at all time points from 2 hours onward (all  ≤ 0.003). Significant improvements versus placebo in PERMP-A and PERMP-C scores were also observed from 2 to 12 hours postdose with d-ATS treatment. d-ATS was safe and well-tolerated, with a systemic safety profile similar to that observed with oral amphetamines. This study demonstrates that d-ATS is an effective and well-tolerated treatment for children and adolescents with ADHD. These data indicate that d-ATS can deliver sustained levels of efficacy along with the advantages of transdermal drug delivery, making it a beneficial new treatment option. NCT01711021.