In this multicentre study we evaluated the prevalence and risk factors of otitis media with effusion (OME) in Italian school-children and the effectiveness of medical treatment of chronic OME with a new cephalosporin, ceftibuten. During two winter periods, 3413 children, aged 5 to 7 years, were examined for the presence of OME by means of pneumotoscopy and a portable, hand-held tympanometer. The prevalence of asymptomatic OME was 14.2%, with no difference as regards sex, age, month of examination or geographic area. Younger children had significantly more bilateral than unilateral effusion. A recent episode of acute otitis media and previous tonsillectomy or adenoidectomy were associated with an increased risk of OME in multivariate logistic regression models. The presence of OME was unrelated to such factors as birthweight, prematurity, sibling or parental history of allergy, duration of daycare attendance, family history of ear infections. After 12 weeks, 26.6% of children with OME still had middle-ear fluid: 52 were randomized to ceftibuten (9 mg/kg q.d. for 14 days) and 59 to no treatment (nasal saline drops allowed). Children treated with ceftibuten had a significantly better resolution of middle-ear effusion after 4 and 8 weeks. As mass screening programmes for OME in the year of school entry are questioned, a focus only on children with known risk factors seems advisable. Ceftibuten can be useful in reducing the duration of middle-ear effusion.