Gaucher's disease (GD) is a hereditary lysosomal storage disease characterized by abnormal deposition of glucocerebroside due to the enzyme glucocerebrosidase deficiency, resulting in multi-organ pathology. GD type III has a progressive neurological involvement. We studied the vestibular and saccadic abnormalities in GD type III to determine if these parameters may be useful for assessing neurological involvement. We evaluated the vestibular and saccadic responses of two siblings with genetically identified GD type III on enzyme replacement therapy. Vestibular functions were assessed with the head impulse test (HIT), vestibular evoked myogenic potentials (VEMPs), and electrical vestibular stimulation (EVS). Saccadic functions were investigated with volitional horizontal and vertical saccades to ±20°. Three-dimensional head and eye movements were recorded with dual-search coils and VEMP with surface electrodes. HIT showed impaired individual semicircular canal function with halved angular vestibulo-ocular reflex (VOR) gains and absent horizontal refixation saccade. Ocular and cervical VEMPs to air-conducted clicks were absent in the older sibling, and only cervical VEMP was present in the younger sibling indicating otolithic dysfunction. EVS showed prolonged onset latency and attenuated tonic and phasic responses suggesting impaired neural conduction and vestibular function. Horizontal saccadic velocity was miniscule (<30°/s) and multiple back-to-back saccades with saccade-vergence interaction were utilized to minimize eye position error in the older sibling. Vertical saccades were slightly abnormal, but vergence and smooth pursuit were normal in both siblings. Our findings suggest that GD affected the vestibular nuclei in addition to the paramedian pontine reticular formation. These vestibular and saccadic abnormalities may be useful biomarkers to monitor neurological deterioration.