Background and Aim: Although for a child to maximize his or her mastery of language, hearing aids (HAs) must consistently be worn, and they must be functioning correctly many studies indicates some hearing- impaired children`s hearing aid do not work perfectly.The purpose of this study was to determine types of defects in students&apos hearing aid (HA) in Tehran Exceptional Schools.

Materials and method: In this cross-sectional analytic study defects in sixty –two HAs of 41 children were determined. All were the students of Exceptional Schools referred to Audiology Clinic, Faculty of Rehabilitation Medical Sciences University of Tehran. Functions of the HAs were first checked by a sthetoclips. Then the electroacoustic measurements performed to determine the values of maximum gain and maximum power output. The data were separately recorded in a questionnaire for each kind of the HAs.

Results: Fifty-six percent of HAs functioned perfectly and forty-four percent were not. The most Frequet defects were 24% and 20% pertained to the battery and manual controls respectively. External components had more difficulties than internal components. Seventy percent of ear molds were damaged. There were significant differences between peak of FOG and MPO curves in the catalogue and electroacoustic measurements in 2cc coupler.

Conclusion: Most damaged parts of HAs in Tehran Exceptional students is related to the battery and controls which are external components of HAs. Because of high rate of dysfunctioning HAs and ear molds in this population in this survey, it is necessary to promote orientation and counseling level after fitting and to develop the quality of HAs and ear molds for Exceptional School students.