Sleep disturbances in children with neurodevelopmental disabilities are common and frequently difficult to treat with conventional pharmacological and behavioural methods. Melatonin is a pineal hormone known to be important in the regulation of the circadian rhythm, including the sleep-wake cycle. This systematic review of available evidence from randomized clinical trials assesses whether melatonin plays a beneficial role in these children and, in particular, its effect on total sleep time, time to sleep onset (sleep latency), and number of awakenings. We also looked at a parental view of the effect. Randomized clinical trials were identified where oral melatonin was compared with a placebo in children with any type of neurodevelopmental disability and associated sleep disturbance. Only three studies, reporting a total of 35 children, fulfilled the criteria for inclusion. The two studies that reported time to sleep onset showed a significant decrease (p<0.05) in this specific outcome where melatonin was compared with a placebo. There was no significant effect of melatonin compared with a placebo on the other outcome measures of total sleep time, night-time awakenings, and parental opinions. Despite the extremely limited randomized clinical trial data, melatonin appears to remain a commonly prescribed drug for disturbed sleep in children with neurodevelopmental abnormalities.