OBJECTIVE: To evaluate the efficacy and safety of melatonin in the treatment of sleep onset insomnia in children and adolescents. METHODS: Electronic databases and bibliographies of relevant reports were searched for randomized, placebo-controlled, clinical trials that used melatonin in children and adolescents with sleep onset insomnia. The quality of the included studies was assessed by the Cochrane Collaboration's risk-of-bias method. The mean differences (MD) and the odds ratios (OR) with 95% confidence interval (CI) were estimated by a random-effects model. Primary outcomes were sleep onset time (SOT), drop-out for all causes and drop-out for adverse events. Secondary outcomes included dim light melatonin onset (DLMO), sleep onset latency (SOL), total sleep time (TST), light-off time, and wake-up time. RESULTS: Seven trials with 387 participants were finally included after a systematic search. The overall quality of the included studies was low to moderate. SOT in patients receiving melatonin advanced more than patients receiving placebo (MD = -0.62 h, 95% CI -0.80, -0.45), as well as DLMO (MD = -0.82 h, 95% CI -1.23, -0.41). No differences were found in the outcome of drop-out for all causes (OR = 1.51, 95% CI 0.57, 4.05) or drop-out for adverse events (OR = 3.35, 95% CI 0.13, 86.03). Severe adverse events, migraine, and mild generalized epilepsy were reported in two cases. SOL decreased and TST increased, MD = -0.36 h (95% CI -0.49, -0.24) and MD = 0.38 h (95% CI 0.09, 0.66), respectively. Light-off time and wake-up time did not differ significantly. CONCLUSIONS: Melatonin was an effective and tolerable drug in the short-term treatment of sleep onset insomnia in children and adolescents. More studies, especially in adolescents, are needed to investigate the efficacy and safety of melatonin.