OBJECTIVE To test the null hypothesis that rapid maxillary expansion (RME) with a rigid bonded appliance has no effect on conductive hearing loss (CHL) in growing children. MATERIALS AND METHODS Fifteen growing subjects (mean age 13.43 +/- 0.86 years) who had narrow maxillary arches and CHL participated in this study. Three pure-tone audiometric and tympanometric records were taken from each subject. The first records were taken before RME (T1), the second after maxillary expansion (T2) (mean = 0.83 months), and the third after retention (mean = 6 months) and fixed appliance treatment (approximately 2 years) periods (T3). The data were analyzed by means of analysis of variance (ANOVA) and least significant difference (LSD) tests. RESULTS Hearing levels of the patients were improved and air-bone gaps decreased at a statistically significant level (P < .001) during active expansion (T2-T1) and the retention and fixed appliance treatment (T2-T3) periods. Middle ear volume increased in all observation periods. However, a statistically significant increase was observed only in the T2-T3 period. No significant change was observed in the static compliance value. CONCLUSIONS The hypothesis is rejected. RME treatment has a positive and statistically significant effect on both improvements in hearing and normal function of the eustachian tube in patients having transverse maxillary deficiency and CHL.