Endolymphatic hydrops (EH) has been reported in ears with otosclerosis. The objective of this study was to investigate the clinical features of ears with otosclerosis and EH on magnetic resonance imaging (MRI) and identify predictors for the presence of EH.Retrospective study.University hospital.Forty-six ears from 37 patients with otosclerosis were included in the present study.The subjects were divided into three groups, those with no, mild, or significant EH, based on 3-T MRI with intravenous injection of gadolinium. Hearing levels and the extent of otosclerotic lesions graded based on the computed tomography (CT) findings were compared among the groups. Moreover, to examine the vascular activity of the disease, intraoperative measurements of blood flow were also evaluated.Imaging, hearing levels, and blood flow values.The overall rate of EH was 58.7% (27 of 46 ears); cochlear EH (52.2%) was more frequent than vestibular EH (26.1%). Average thresholds in ears with significant EH were significantly higher at several frequencies, both on air and bone conduction, than those with no or mild EH. Significant EH was more frequently observed in ears with advanced stages on CT than in those without advanced stages. The values of blood flow in the area anterior to the oval window were higher in some ears with EH than in ears without EH.EH was frequently present in ears with otosclerosis, especially those with severe hearing loss or advanced disease on CT.