The prevalence of otitis media with effusion (OME) and environmental risk factors were investigated in 423 children aged 7 -12 years at three primary schools in Princes' Islands, Istanbul, Turkey. An ear, nose and throat examination, including tympanometry, was performed in April (end of the school year) and the families completed a questionnaire about potential risk factors. Type B or C2 tympanograms were taken as indicating OME. The overall prevalence of OME was 16%. OME was significantly associated with numbers of episodes of upper respiratory tract infections (URTI) and acute otitis media (AOM) during the previous year, class size and snoring, but not with allergic symptoms, kindergarten years, breastfeeding duration, parental smoking, domestic animals at home, numbers of siblings and family members, type of home heating, parents' educational level or monthly income. Four or more URTIs and two or more AOM episodes in a year, snoring and class size larger than 20 were risk factors for OME.