Objective Sleep problems are experienced by 25-30 percent of children and adolescents, regardless of age. The purpose of this study was to investigate if there is any relationship between gender or school entrance and sleep complaints. Methods From June 2008 to May 2009 children aged 2 to 12 years were selected by clustered randomization of families. The Persian version of the BEARS questionnaire (Bedtime problems, Excessive sleepiness, Awakenings during the night, Regularity of sleep, Snoring) with five domains was filled out by general pediatricians. Prevalence of sleep complaints in each B-E-A-R-S category was calculated and compared for pre-school and school-age groups. Findings BEARS questionnaire was completed for a total of 746 children (2-12 years old); 325 in pre-school-age group (2-6 years old) (142 females [43.7%] and 183 males [56.3%]) and 421 in primary school-age group (7-12 years old) with the average age of 3.93 (±0.16) years and 9.63 (±0.16) years respectively. The most common screening problem in both groups was excessive daytime sleepiness (64.9% and 62.9% respectively). Bedtime problems and also regularity and duration of sleep were significantly more prevalent in pre-school-age group (P<0.0002; odds ratio [OR] =1.98; 95% confidence interval [95%CI]: 1.98-4.20; and OR=2.00; 95%CI: 1.41- 2.84 respectively). The difference between mean sleep duration between pre-school age and school-age groups was statistically significant (P<0.0001). Conclusion The current survey shows that different types of sleep problems are relatively high especially in the form of excessive daytime sleeping domain in preschool- and school-aged children. Bedtime problems and regularity problems were significantly more prevalent in pre-school-age group. School entrance seems to play a positive role for bedtime problems, and sleep-disordered breathing.