Sleep disturbances is a distressing and disabling condition that affects many people, and can affect on quality of work and education of MEDICAL STUDENTS AND RESIDENTS. The objective of this study was to determine the prevalence of sleep disorders in MEDICAL STUDENTS AND RESIDENTS. A representative sample of MEDICAL STUDENTS AND RESIDENTS of Iran University of medical students in Tehran, Iran, were assessed by a self-administered questionnaire. This study covers 400 medical students from the first to seventh year and residents from the first to the last year between December 2007 and February 2008. The questionnaire includes questions on demographic characteristics (6 questions), sleep/wake habits (6 questions), INSOMNIA-related symptoms (4 questions), symptoms of PARASOMNIA (6 questions), cognitive and psychomotor behaviors (6 questions), lifestyle (4 questions), self-perception of sleep satisfaction, and use of sleeping pills (2 questions). The sample included 135 (33.8%) pre-internship students, 150 (37.5%) interns, and 115 (28.7%) medical residents. Sleep satisfaction was reported as “perfect” in only 14%. 44% and 30% reported “good” and “fair” satisfaction. The use of sleeping pills in the previous 30 days was reported by only 3.3% of respondents. One hundred and three (25.7%) participants reported working while studying (sometimes to full-time). Between 43% and 48% of participants had gone to bed later than usual one to three times a week. About 14% of subjects reported snoring. The mean±SD of INSOMNIA and PARASOMNIA scales were 7.0±2.3 and 6.8±1.2, respectively. The mean of INSOMNIA were more among females, subjects with noise in their living place, and students who worked full-time while studying, and was less in person who did exercise (P< 0.05). Sleep disturbances are an important issue among MEDICAL STUDENTS AND RESIDENTS and associated with age, gender, living conditions, doing exercise, and WORKLOAD.