Acoustic neuromas occur in two forms: sporadic and those associated with Neurofibromatosis Type II (NF II).

Approximately 95% of all acoustic neuromas are sporadic cases and are unilateral (affecting one ear). Patients with sporadic acoustic neuromas tend to begin having symptoms in middle age with the average being around fifty years old at diagnosis.

In contrast, those tumors associated with NF II are bilateral (affecting both ears) and account for approximately 5% of acoustic neuroma patients. NF II is a rare, genetic condition that affects one in 100,000 people in the United States. Patients with NFII develop benign tumors on both auditory nerves and may have to have both hearing nerves severed through tumor removal. Patients with NF II present at a younger age averaging around thirty years old when they first develop symptoms.