Within a period of two years, we were able to observe five cases in which non-organic (functional) hearing defects occurred during infancy. The careful assessment of the case history and close observation, but also a differential-diagnostic audiological procedure in case of unstable hearing defects of unknown origin may disclose non-organic auditory communication disturbances. Based on our experience, the easily appreciated clinical picture is described. A pointer is supplied by the unstable auditory threshold in the tone audiogram. Integration of impedance audiometry and of acoustically evoked potentials (brain stem audiometry) into the individual audiometric experimental pattern is indispensable. In differential diagnosis it is essential to take into account fluctuating diseases of the internal ear, as well as high-grade auditory inattention as an expression of a partial conduction impairment.