The thorough investigation of patients presenting with sudden or fluctuating hearing loss, ringing or vertigo includes serology to exclude otosyphilis. Treatment of otosyphilis with penicillin and corticosteroids has achieved improvement in hearing, tinnitus and vertigo, but not in all patients. Selecting which patient with positive serology will benefit from treatment remains a difficult clinical problem. All patients presenting to The New York Eye and Ear Infirmary with cochleovestibular dysfunction of unknown aetiology and positive syphilis serology were assumed to have otosyphilis and were treated with intravenous penicillin, if non-allergic, and steroids. Lumbar puncture and HIV testing were performed. Eighteen patients were treated. Hearing (SRT and/or discrimination) improved in 4 of 16 patients with hearing loss (25%), tinnitus decreased in 10 of 14 (71%) and dysequilibrium improved in 6 of 9 (66%). Factors associated with a good response included fluctuating symptoms, especially hearing, hearing loss less than five years, and age less than 60. Improvement was unrelated to the severity of the loss or previous therapy. Patients with CSF abnormalities, including two patients with HIV disease, had subjective improvement. A summary of our results and a treatment protocol are presented.