Effectiveness and tolerability of melatonin was assessed in 32 children (mean age 9.6 +/- 4.5 years) with chronic sleep initiation and sleep maintenance problems treated naturalistically in a pediatric sleep medicine center. Children received melatonin for an average of 2.1 +/- 2.0 months at a final average dose of 2.0 +/- 1.2 mg administered 1 hour before bedtime. Twenty-nine (90.6%) children exhibited partial improvement to complete resolution of their sleep problems as measured by sleep latency time and number of awakenings reported by parents. Thus, melatonin may be effective, safe, and well tolerated in the treatment of chronic insomnia in children.