Abstract. Insomnia is a widespread pathological condition in the general population, which has numerous social and medical consequences. Sleep disorders in patients with chronic mercury intoxications are much more common than in the general population. This study aimed to determine the most significant differential diagnostic criteria for sleep disorders in patients with chronic mercury intoxications for their further effective treatment. In this regard, we examined 30 patients with chronic mercury intoxications, whose age averaged 56 0.71 years, and 30 patients of the control group, whose age averaged 54 0.66. All patients underwent clinical, neurological, polysomnographic, and psychological examinations, and neurotransmitters were determined in the blood. Discriminant analysis based on polysomnography, psychological testing and neurotransmitter metabolism revealed significant differences in the examined groups of patients for the following indicators: total sleep time (decreased in the chronic mercury intoxication group) and wake within sleep (increased in the chronic mercury intoxication group) based on polysomnography, blood dopamine level (increased in the chronic mercury intoxication group) as well as reactive anxiety level according to the Spielberger-Khanin scale (increased in the chronic mercury intoxication group). Taking into account the data obtained, it is possible to improve approaches to the diagnosis and treatment of insomnia in the presence of chronic mercury intoxication.