Background: Insomnia is a distressing and disabling condition affecting not only many people's quality of life and work but also their psychosocial conditions. Therefore, this research has done to survey insomnia prevalence among 18 years old people and over in Kashan city in 2008.

Materials and Methods: This cross-sectional research has performed done in Kashan using randomized sampling (N=1155). The research tools contain demographic characteristics questionnaire and insomnia questionnaire based on DSM-IV criteria including difficult falling asleep, staying asleep and daytime sleepiness. Its validity was confirmed by five psychiatrists the reliability of this questionnaire with test-retest method was 99%. The data were analyzed via Chi square, Fisher exact test and OR, CI. Results: Of 1155 persons, 684 (59.2) had insomnia problem. Insomnia problem is extremely prevalent among those who were between 41 to 65 years old (266 of persons 67.9) and women (387 of persons 56.5). This study showed that there was a significant relationship between insomnia problem and mental disorder history [P<0/0001, OR=2.24], sleep disorder in family history [P<0/0001, OR=4.67] and drinking caffeine before sleep [P<0/001, OR=1.64]. Conclusion: According to this study, most people studied suffer from insomnia problem, particularly women and middle aged people. Since insomnia can be a risk factor for onset of depression and anxiety disorders, and increases direct and indirect medical costs among other consequences it is necessary to prepare an exact schedule for resolving this problem and improving sleep quality.