To describe unilateral hearing loss preceding brainstem infarction due to basilar artery occlusion. Clinical capsule report. University hospital. A 67-year-old woman presented with unilateral acute hearing loss with dizziness as a sole prodromal manifestation of basilar artery occlusion for 2 weeks before the appearance of motor and oculomotor deficits. Otologic examinations and magnetic resonance imaging (MRI) were performed. A pure-tone audiogram showed unilateral profound sensorineural hearing loss preceding brainstem occlusion. Diffusion-weighted MR image demonstrated acute infarction around the paramedian area of the upper and middle pons, although T2-weighted MR image showed a normal brain image except for occlusion of the basilar artery. Acute unilateral hearing loss could be a prodrome of basilar artery occlusion. Clinicians must consider this possibility, especially in patients at high risk of brainstem infarction.