Clinical observations supplemented with imaging examination show that the large vestibular aqueduct syndrome (LVAS) is a rare developmental anomaly of the inner ear, which leads to hearing loss. The authors present a case history, results of imaging examination (high resolution CT, MRI), results of hearing acuity examinations (tonal audiometry, otoacoustic emissions, brainstem auditory evoked potentials) and results of balance examinations (videonystagmography) in an 11-year-old boy suffering from deep mixed progressive hearing loss of the right ear due to head trauma. The aim of this paper is to specify the most typical clinical, radiological and anatomopathological manifestations of this pathology of the inner ear. The authors describe the diagnostic and identification difficulties associated with the mixed hearing loss observed in this case. The article also discusses the child's activity limitations, which should be taken into account once diagnosis of this rare labyrinthine pathology is established.