We describe a rare case of an acoustic tumor diagnosed in a 69-year-old female who presented with a history of persistent rotatory vertigo on shifting her head position since several weeks, which was accompanied by mixed upper eyelid-oriented counterclockwise rotation on standing. Pure-tone audiometry and auditory brainstem responses were symmetrical, and thermal stimulus test results were normal. These symptoms ruled out Meniere’s disease and acute vestibular neuronitis; therefore, benign paroxysmal positional vertigo (BPPV) of the right posterior canal was considered the most probable cause. However, no improvement was observed with the Epley maneuver. Furthermore, the eye-tracking test indicated ataxia, and optokinetic nystagmus was also abnormal, which warranted further examination using magnetic resonance imaging (MRI). T2-weighted images revealed a 5-mm tumor within the internal acoustic meatus. This case strongly suggests that MRI should be considered for all patients presenting with atypical nystagmus, even when BPPV is the most probable cause.