The effects of rapid maxillary expansion (RME) on conductive hearing loss were investigated in 14 subjects (11 females and 3 males). The subjects ranged in age from 10 years 4 months to 16 years 9 months (mean age 12 years 11 months +/- 1 year 9 months) and had narrow maxillary arches and conductive hearing loss. Hearing levels were determined by means of pure-tone audiometric records. Three records were taken for each subject. The first was taken before RME, the second after sufficient midpalatal suture opening was achieved (mean = 15 days), and the third after the retention period (mean = 4.5 months). All the audiometric records were assessed by an otolaryngologist. Changes in both hearing level and air-bone gap were investigated by means of analysis of variance. It has been determined that hearing improved at a statistically significant level (P < 0.05) after the active treatment period, but that the improvement reversed at the end of the retention period. Five patients experienced significant and stable hearing improvement over the duration of this study.