Otitis media with effusion (OME) is a frequent paediatric disorder. The condition is often asymptomatic, and so can easily be missed. However, OME can lead to hearing loss that impairs the child's language and behavioural development. The diagnosis is essentially clinical, and is based on otoscopy and (in some cases) tympanometry. Nasal endoscopy is only indicated in cases of unilateral OME or when obstructive adenoid hypertrophy is suspected. Otitis media with effusion is defined as the observation of middle-ear effusion at consultations three months apart. Hearing must be evaluated (using an age-appropriate audiometry technique) before and after treatment, so as not to miss another underlying cause of deafness (e.g. perception deafness). Craniofacial dysmorphism, respiratory allergy and gastro-oesophageal reflux all favour the development of OME. Although a certain number of medications (antibiotics, corticoids, antihistamines, mucokinetic agents, and nasal decongestants) can be used to treat OME, they are not reliably effective and rarely provide long-term relief. The benchmark treatment for OME is placement of tympanostomy tubes (TTs) and (in some cases) adjunct adenoidectomy. The TTs rapidly normalize hearing and effectively prevent the development of cholesteatoma in the middle ear. In contrast, TTs do not prevent progression towards tympanic atrophy or a retraction pocket. Adenoidectomy enhances the effectiveness of TTs. In children with adenoid hypertrophy, adenoidectomy is indicated before the age of 4 but can be performed later when OME is identified by nasal endoscopy. Children must be followed up until OME has disappeared completely, so that any complications are not missed.