ObjectivesTo determine the incidence of middle ear abnormalities in patients with bilateral otosclerosis, which could potentially affect successful stapedectomy, and the rates of success in these patients, including the chance of overclosure in the second ear.Study DesignRetrospective case review of operative and audiologic records.SettingPrivate otology practice.PatientsOne thousand eight hundred patients underwent 3,600 primary stapedectomies for bilateral otosclerosis.InterventionAnalysis of perioperative and follow-up audiograms with associated operative findings, including obliterative otosclerosis and solid footplates, dehiscent or overhanging facial nerve, narrow oval window niche, promontory overhang, and ossicular fixation or malformation.Main Outcome MeasuresAudiologic stapedectomy success was determined as overclosure or closure of preoperative air-bone gap to less than 10 dB at 1 year or more of follow-up.ResultsThe rate of finding any abnormality was 25%. Abnormalities present bilaterally were found in 135 patients (7%), with otosclerosis requiring an oval window drillout as the most common finding (41%), followed by dehiscent or overhanging facial nerves (25%). Success in patients with abnormalities was 78% overall, with bilateral overclosure in 40%.ConclusionsAbnormal middle ear findings during stapedectomy occur in a significant percentage of patients. Reasonable rates of success and overclosure can still be expected, but this is somewhat finding-specific. The predictive value of these findings, the associated rates of success with potential impact on surgical counseling, and planning for the “other ear” are discussed.