IMPORTANCE: Sleep disturbance is common in children with atopic dermatitis (AD), but effective clinical management for this problem is lacking. Reduced levels of nocturnal melatonin were found to be associated with sleep disturbance and increased disease severity in children with AD. Melatonin also has sleep-inducing and anti-inflammatory properties and therefore might be useful for the management of AD. OBJECTIVE: To evaluate the effectiveness of melatonin supplementation for improving the sleep disturbance and severity of disease in children with AD. DESIGN, SETTING, AND PARTICIPANTS: This randomized clinical trial used a double-blind, placebo-controlled crossover design to study 73 children and adolescents aged 1 to 18 years with physician-diagnosed AD involving at least 5% of the total body surface area. The study was conducted at the pediatric department of a large tertiary care hospital in Taiwan from August 1, 2012, through January 31, 2013. Forty-eight children were randomized 1:1 to melatonin or placebo treatment, and 38 of these (79%) completed the cross-over period of the trial. Final follow-up occurred on April 13, 2013, and data were analyzed from January 27 to April 25, 2014. Analyses were based on intention to treat. INTERVENTIONS: Melatonin, 3 mg/d, or placebo for 4 weeks followed by a 2-week washout period and then crossover to the alternate treatment for 4 weeks. MAIN OUTCOMES AND MEASURES: The primary outcome was AD severity evaluated using the Scoring Atopic Dermatitis (SCORAD) index, with scores ranging from 0 to 103 and greater scores indicating worse symptoms. Secondary outcomes included sleep variables measured by actigraphy, subjective change in sleep and dermatitis, sleep variables measured by polysomnography, nocturnal urinary levels of 6-sulfatoxymelatonin, and serum IgE levels. RESULTS: After melatonin treatment among the 48 children included in the study, the SCORAD index decreased by 9.1 compared with after placebo (95% CI, -13.7 to -4.6; P < .001), from a mean (SD) of 49.1 (24.3) to 40.2 (20.9). Moreover, the sleep-onset latency shortened by 21.4 minutes after melatonin treatment compared with after placebo (95% CI, -38.6 to -4.2; P = .02). The improvement in the SCORAD index did not correlate significantly with the change in sleep-onset latency (r = -0.04; P = .85). No patient withdrew owing to adverse events, and no adverse event was reported throughout the study. CONCLUSIONS AND RELEVANCE: Melatonin supplementation is a safe and effective way to improve the sleep-onset latency and disease severity in children with AD. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01638234.