Melatonin prolonged release (PR) 2 mg is approved for the treatment of primary insomnia characterized by poor sleep quality in patients aged ≥55 years in the EU and elsewhere. Patients may receive treatment with melatonin PR for up to 13 weeks. Production of endogenous nocturnal melatonin, which helps regulate circadian rhythm, may be decreased in older adults. Administration of melatonin PR 2 mg 1-2 h before bedtime mimics the natural secretion pattern of melatonin, thereby leading to improvements in the circadian regulation of the sleep-wake cycle. In older adults, melatonin PR 2 mg had no effect on psychomotor functions, memory recall or driving skills during the night or the next morning relative to placebo, and was associated with significantly less impairment on many of these tasks relative to zolpidem 10 mg alone or in combination with melatonin PR 2 mg. In 3-week and 6-month, randomized, double-blind clinical trials in patients with primary insomnia aged ≥55 years, melatonin PR 2 mg 1-2 h before bedtime was associated with significant improvements relative to placebo in many sleep and daytime parameters, including sleep quality and latency, morning alertness and health-related quality of life. Melatonin PR 2 mg was very well tolerated in clinical trials in older patients, with a tolerability profile that was similar to that of placebo. Short- or longer-term treatment with melatonin PR 2 mg was not associated with dependence, tolerance, rebound insomnia or withdrawal symptoms.