Importance Dupilumab subcutaneous injection is approved for treating moderate-to-severe atopic dermatitis (AD) in adolescents, but there has been too little research on an efficacious systemic oral treatment with a favorable benefit-risk profile for adolescents with moderate-to-severe AD.Objective To investigate the efficacy and safety of oral abrocitinib plus topical therapy in adolescents with moderate-to-severe AD.Design, Setting, and Participants The phase 3, randomized, double-blind, placebo-controlled study JADE TEEN was conducted in countries of the Asia–Pacific region, Europe, and North America in patients aged 12 to 17 years with moderate-to-severe AD and an inadequate response to 4 consecutive weeks or longer of topical medication or a need for systemic therapy for AD. The study was conducted between February 18, 2019, and April 8, 2020. The data were analyzed after study completion.Interventions Patients were randomly assigned 1:1:1 to receive once-daily oral abrocitinib, 200 mg or 100 mg, or placebo for 12 weeks in combination with topical therapy.Main Outcomes and Measures Coprimary end points were achievement of an Investigator’s Global Assessment (IGA) response of clear (0) or almost clear (1) with improvement of 2 or more grades from baseline (IGA 0/1) and 75% or greater improvement from baseline in Eczema Area and Severity Index (EASI-75) response at week 12. Key secondary end points included 4-point or greater improvement in Peak Pruritus Numerical Rating Scale (PP-NRS4) at week 12. Adverse events (AEs) were monitored.Results This study included 285 adolescents with moderate-to-severe AD (145 boys [50.9%] and 140 girls [49.1%]), of whom 160 (56.1%) were White and 94 (33.0%) were Asian; the median age was 15 years (interquartile range 13-17 years). Substantially more patients treated with abrocitinib (200 mg or 100 mg) vs placebo achieved an IGA response of 0/1 (46.2%; 41.6% vs 24.5%; P < .05 for both), EASI-75 (72.0%; 68.5% vs 41.5%; P < .05 for both), and PP-NRS4 (55.4%; 52.6% vs 29.8%; P < .01 for 200 mg vs placebo) at week 12. Adverse events were reported for 59 (62.8%), 54 (56.8%), and 50 (52.1%) patients in the 200 mg, 100 mg, and placebo groups, respectively; nausea was more common with abrocitinib, 200 mg (17 [18.1%]) and 100 mg (7 [7.4%]). Herpes-related AEs were infrequent; 1 (1.1%), 0, and 2 (2.1%) patients had serious AEs.Conclusions and Relevance This randomized clinical trial found that oral abrocitinib combined with topical therapy was significantly more effective than placebo with topical therapy in adolescents with moderate-to-severe AD, with an acceptable safety profile.