A number of diseases of the middle ear are summed up under the term otitis media: acute otitis media, recurrent acute otitis media, otitis media with effusion, chronic suppurative otitis media and chronic otitis media epitympanalis (= cholesteatoma). Acute otitis media belongs to the most common pediatric diseases and is often caused by bacterial infection. Since the advent of pneumococcal vaccines the quantity of AOM caused by pneumococci has declined; vaccination against NTHi and Moraxella catarrhalis are being developed. Main pillar of conservative treatment of AOM is symptomatic therapy of otalgia and fever as well as restoring the Eustachian tubal function. When indicated, amoxicillin represents antibiotic medication of choice. Acute mastoiditis, facial nerve paresis, labyrinthitis, Gradenigo syndrome, sinus vein thrombosis, meningitis and brain abscess belong to the complications of AOM among others. Both innate and adaptive immune system are involved in recovery of OM with innate immunity playing a critical role. Dysfunction of the Eustachian tube often underlies OM. Manometric measurement of Eustachian tube function may be useful for indication of balloon Eustachian tuboplasty. Several theories explain pathogenesis of cholesteatoma and multiple pro-inflammatory processes promote its progress in the course of the disease.