Patients with acoustic neuroma may have sudden sensorineural hearing loss. Most patients with sudden hearing loss seek medical attention promptly, but the diagnosis of an acoustic neuroma may be delayed for months or years because sudden hearing loss is an unusual initial symptom of an acoustic neuroma. In a retrospective review of 836 cases of sudden hearing loss, we found 13 patients with acoustic neuromas. The prevalence of acoustic neuromas for those screened with auditory brain stem response or magnetic resonance imaging was 2.5%. In addition to these 13 patients, 79 acoustic neuroma patients treated in our clinic had well-documented sudden hearing loss as the initial symptom. Hearing loss in these 92 patients ranged from mild to profound. Associated symptoms of pain, facial paresthesia, or unilateral tinnitus preceding the sudden hearing loss were suggestive of an acoustic neuroma, as was a midfrequency (U-shaped) hearing loss. A history of other diseases or events that might explain the sudden hearing loss, a normal electronystagmogram, or recovery of hearing does not eliminate the possibility of a tumor. Because there are no clinical findings that clearly distinguish those patients with acoustic neuromas from other patients with sudden hearing loss, we recommend either an evaluation with auditory brain stem response or gadolinium-enhanced magnetic resonance imaging for any patient with sudden hearing loss.