INTRODUCTION Insomnia became an object of concern in Aristotelian times, when he wrote a monograph on sleep disorders (350 BC). Although community of science and medicine has been interested in sleep disorders for almost 2000 years, however, there are not much information about the prevalence of insomnia, especially among citizens of developing countries. Epidemiological information about prevalence of insomnia and sleep complaints varies in different countries [Roth et.al., 1996], because of diversity of methodology for data collection. According to data of research carried out in the United States of America, Europe and Australia, 10–49% of population are not satisfied with their sleep quality. [Walsh, Ustun, 1999]. According to data of lifestyle research in Lithuania (1996), insomnia was a problem for 22.5% of male (from 20 to 64 years old) and 29.3% of female [Grabauskas, Klumbienė, 1998]. Sleep complaints among Lithuanian citizens have not been researched up to now, although, as foreign scientists maintain, sleep disorder can accelerate development of many somatic as well as mental diseases, besides, after a few sleepless nights, follows irritability, decrease of efficiency, it is difficult to concentrate, considerably increases risk of traffic accidents or accidents at work [Balter, Uhlenhuth, 1992]. Supposedly, there is a connection among heart and vascular diseases, sleep disorders and depression [Mahowald et.al., 1989]. Research that was carried out abroad proved... [to full text]