OBJECTIVE Acute unilateral peripheral-vestibular hypofunction (UVH) shifts the subjective visual vertical (SVV) ipsilesionally, triggering central compensation that usually eliminates shifts when upright. We hypothesized that compensation is worse when roll-tilted. METHODS We quantified SVV errors and variability in different roll-tilted positions (0°, ±45°, ±90°) in patients with chronic UVH affecting the superior branch (SVN; n=4) or the entire (CVN; n=9) vestibular nerve. RESULTS Errors in SVN and CVN were not different. When roll-tilted ipsilesionally 45°(9.6±5.4°vs. -0.2±6.4°, patients vs. controls, p<0.001) and 90°(23.5±5.7°vs. 16.8±8.8°, p=0.003), the patient's SVV was shifted significantly towards the lesioned ear. When upright, only a trend was noted (3.6±2.2°vs. 0.0±1.2°, p=0.099); for contralesional roll-tilts shifts were not different from controls. Variability was larger for CVN than SVN (p=0.046). With increasing disease-duration, adjustment errors decayed for ipsilesional roll-tilt and upright (p0.025). CONCLUSIONS The reason verticality perception was distorted for ipsilesional roll-tilts, may be the insufficient integration of contralesional otolith-input. Similar errors in SVN and CVN suggest a dominant utricular role in verticality perception, albeit the sacculus may improve precision of SVV estimates. SIGNIFICANCE With deficiencies in central compensation being roll-angle dependent, extending SVV-testing to roll-tilted positions may improve identifying patients with chronic UVH. Highlights:• Visual vertical (VV) was measured in 13 patients with chronic unilateral vestibular hypofunction.• VV shifts in the patients were significant only when rolled ipsilesionally.• Thus VV testing in roll-tilted positions is recommended to identify more subtle vestibular deficits. 3 AbstractObjective: Acute unilateral peripheral-vestibular hypofunction (UVH) shifts the subjective visual vertical (SVV) ipsilesionally, triggering central compensation that usually eliminates shifts when upright. We hypothesized that compensation is worse when roll-tilted. Methods