Otitis media may be the result of Eustachian tube dysfunction or inflammation of the middle ear, or both. The Eustachian tube may be either abnormally patent (patulous or semipatulous) or, more commonly, obstructed. Functional obstruction is most likely due to either lack of tubal stiffness or an abnormal active opening mechanism, e.g., inefficient tensor veli palatini muscle. Mechanical obstruction may be secondary to extrinsic causes such as a nasopharyngeal tumor or possibly an adenoid mass. Intrinsic obstruction can result from an upper respiratory tract infection. Even though proof that allergy is causally related to otitis media is lacking, recent studies indicate that the Eustachian tube can become partially obstructed when upper respiratory allergy is present. In addition, there is now some evidence that in a small percentage of children with upper respiratory allergy, the middle ear may be a "shock organ." Future studies are needed to define the role of allergy in the pathophysiology of the Eustachian tube and the pathogenesis of otitis media. Randomized clinical trials will be required to determine the efficacy of the currently popular forms of immunotherapy and allergy control in the prevention of otitis media.