Recognized causes of high-frequency sensorineural hearing loss (SNHL) after tympanoplasty with and without mastoidectomy include acoustic trauma from manipulation of the ossicles, the noise generated by suctioning and, in the case of mastoidectomy, the noise generated by temporal bone drilling. We conducted a retrospective study to identify the effects of ossicular manipulation and mastoid drilling on high-frequency SNHL. Our study population was made up of 51 patients-20 males and 31 females, aged 10 to 59 years (mean: 28.5). Of this group, 26 patients had undergone a unilateral over-under tympanoplasty only (tympanoplasty group) and 25 had undergone a unilateral tympanoplasty plus additional mastoid surgery (mastoidectomy group). Bone-conduction audiograms were obtained pre- and postoperatively; the latter were obtained within 24 hours after surgery and again at 6 months of follow-up. In the tympanoplasty group, a significant SNHL, primarily at 2 kHz, was seen in 6 patients (23%) at 24 hours, but at 6 months there was no depression of bone-conduction thresholds. In the mastoidectomy group, a significant SNHL, primarily at 2 and 4 kHz, occurred in 12 patients (48%) at 24 hours, and bone-conduction deterioration was still present in 4 patients (16%) 6 months after surgery. The difference between the preoperative audiograms and the 6-month audiograms in both groups was statistically significant (p = 0.034). We conclude that (1) over-under tympanoplasty, which requires significant manipulation of the ossicles, can cause temporary SNHL after surgery, and (2) prolonged exposure to the noise generated by mastoid drilling can result in permanent SNHL.