Large vestibular aqueduct syndrome (LVAS) is characterized by a history of recurrent episodes of dizziness and progressive hearing loss. Although underlying equilibrium dysfunction has been speculated in LVAS patients and may be an important factor in selecting patients who should undergo CI, few studies have reported on the prevalence of equilibrium dysfunction in LVAS patients. This study was aimed at determining the frequency of equilibrium dysfunction in LVAS patients and investigating its association with other clinical features. We assessed the equilibrium function in LVAS patients who underwent CI at our institution between January 1999 and December 2016, by the caloric reflex test and/or measurement of the cervical vestibular evoked myogenic potential (cVEMP). Among the 26 ears of the 13 patients included, the caloric reflex test was conducted for 21 ears of 11 patients, while cVEMP measurement was conducted for 23 ears of 12 patients. The caloric reflex test revealed equilibrium dysfunction in 33% (7 of 21) of the examined ears, with 2 patients showing bilateral areflexia, 2 patients showing unilateral areflexia, and 1 patient showing unilateral hyporeflexia. cVEMP measurement revealed equilibrium dysfunction in 4.3% (1 of 23) of the examined ears, with 1 patient showing unilateral hyporeactivity. In total, 38.7% (8 of 26) of the ears examined showed abnormal findings on either the caloric reflex test or cVEMP measurement. Among the 6 patients who presented with a history of episodes of dizziness, 5 showed equilibrium dysfunction on either the caloric reflex test or cVEMP measurement; however, none of the 7 patients with no history of episodes of dizziness showed equilibrium dysfunction on either the caloric reflex test or cVEMP measurement. A significant correlation was observed between a history of episodes of dizziness and the presence of equilibrium dysfunction as assessed by the caloric reflex test or cVEMP measurement. A history of episodes of hearing fluctuation, the hearing loss levels, and the diameter of the vestibular aqueduct were not significantly correlated with the findings of the caloric reflex test or cVEMP measurement. Since approximately 40% of LVAS patients were found to have equilibrium dysfunction, the caloric reflex test or cVEMP measurement are recommended prior to CI, especially among LVAS patients presenting with episodes of dizziness.