Relevance. Sleeplessness is a non-motor disorder that reduces the daily activity of patients with Parkinson’s disease.Intention. To evaluate the effectiveness of the drug “Melaxen” (melatonin) in the treatment of patients with sleep disorders and daytime sleepiness in patients with Parkinson’s disease and previous radiation exposure.Methodology. Fifty patients with Parkinson’s disease (Stage I–II according to Hen-Yar, duration of 3.5 to 6.5 years), previous radiation exposure and current sleep disorders were examined. On average, patients aged (65.8 ± 5.8) years. Most of them were employees of various departments of the Russian Emercom and Defense Ministry. On average, 38 male patients spent (56.1 ± 27.0) days in the area of radiation exposure, with exposure dose of (21.4 ± 11.9) roentgen equivalent man (rem). Female patients-inhabitants of radiation contaminated areas most likely received mean effective dose of 9 mSv (0.9 rem) per person. During treatment of Parkinson’s disease with “Levodopa” in the average daily dosage of (562.5 ± 62.5) mg (stable dose after the start of melatonin), 39 (78 %) of them also received dopamine receptor agonists at a dose of (1.0 ± 0.25) mg / day, the drug Melaxen (melatonin) was used to correct sleep disordersfor over 28 days at a daily dose of 3 mg taken 30–40 minutes before sleep daily. The clinical and psychological state of the patients was studied twice before and after completion of the course of treatment using scales to study the quality and individual significance of sleep, the hospital anxiety and depression scale (HADS), certain cognitive tests and individual sleep diaries.Results and Discussion. According to the clinical and psychological tests, Melaxen (melatonin) contributed to improving the quality of sleep, mental well-being, activity, some cognitive functions, reducing daytime sleepiness and anxiety. The optimization of the mental state was also reflected in the personal diaries of sleep quality. A number of indicators only tended to improve, probably due to short-term studies.Conclusion. In patients with Parkinson’s disease, “Melaxen” was associaeted with improved sleep quality, decreased daytime sleepiness and severity of anxiety and depression, and also increased concentration.