Background: It has been estimated that 20% of adults and children have sleep disorder symptoms and signs. Sleep disordersremain largely undiagnosed in the general population. Increasing evidence suggests that sleep alterations could favor subsequent depressionand behavioral disturbances. Aim of the study: Regarding high prevalence of sleep disorders in the general population and their effect onmental and physical functions, this study was aimed to assess the prevalence of sleep disorders among medical students in KermanshahUniversity of Medical Sciences. Methods: Assessment of sleep disorders was done by Global Sleep Assessment Questionnaire (GSAQ). Inthis descriptive study, frequency of insomnia, daytime sleepiness, non-idiopathic insomnia, obstructive sleep apnea, restless leg syndrome andparoxysmal leg movement, nightmares, sleep walking and a sense of depression or anxiety was calculated. Results: A total number of 393medical students, 151 male and 242 female, were recruited. One or more kinds of sleep disorders have been reported by 254 persons (64%).The most frequent disorder was non-idiopathic insomnia (50.9%). Frequency of idiopathic insomnia was 29.5%. Prevalence of daytimesleepiness was 21.4%. The least frequent disorder was sleep walking (1.5%). Subjective sense of anxiety or depression was reported by 109persons (27.7%). Only 39 (9.9%) of the respondents had no disorder. Conclusion: Our findings suggest that sleep disorders are frequent inour studied population of medical students. More education about sleep disorders, sleep hygiene, and management of a life style whichnecessarily includes shift work and long hours of study, may lead to improved sleep patterns in medical students.