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.