Fifty-six patients with unilateral brainstem infarctions presenting with skew deviation of the eyes were analyzed for static vestibular function in the roll plane. Ischemic lesions were allocated to the level and side of the brainstem by the clinical syndrome and neuroimaging. Two findings of clinical relevance were obtained: (1) All skew deviations were ipsiversive (ipsilateral eye was undermost) with caudal pontomedullary lesions and contraversive (contralateral eye was lowermost) with rostral pontomesencephalic lesions. (2) All skew deviations were associated with concomitant ocular torsion and tilts of subjective visual vertical toward the undermost eye. Thus, skew deviation or more correctly, ocular skew torsion is a sensitive brainstem sign of localizing and lateralizing value. Evidence is presented that the ocular skew torsion sign indicates a vestibular tone imbalance in the roll plane secondary to graviceptive pathway lesions.