A flat tympanogram predicts a middle ear effusion in about 90% of cases. This paper describes how to perform tympanometry, some common problems when doing it and how to classify the curves in normal (type A), middle ear effusion (type B) or negative pressure (type C). The theoretical background of impedance audiometry is outlined. The stapedius reflex, pneumatic otoscopy, reflexometry and otomicroscopy are described as supplements or alternatives in diagnosing fluid in the middle ear. Tympanometry is recommended as a diagnostic modality for general practitioners.