To study the vestibular function and delayed endolymphatic hydrops in patients with profound hearing loss of early childhood, 50 patients (male 28, femals 22) were selected on the basis of the questionnaire, interview and pure tone audiometry among patients presenting dizziness or hearing loss in our clinic from 1990 to 1993. Non-progressive, unilateral, severe to profound sensorineural hearing loss in early childhood(age of one to six) without central neurologic disorders were the selection criteria of these patients Spontaneous, gaze, head shaking and bithermal caloric nystagmus tests were performed using electronystamography. The results were as follows ; 1) Spontaneous nystagums in 10%, head shaking nystagmus in 64% and reduced caloric response in 82% of patients were detected. Reduced caloric response was present on the side of hearing loss in 81%, on the opposite side to hearing loss in 17% and on the both side in 2% of 41 patients. 2) Delayed endolymphatic hydrops was present in 34% of patients and was ipsilateral in 94%, contralateral in 6% of 17 patients. 3) Incidence of head shaking nystagums was significantly higher in delayed endolymphatic hydrops group than non-hydrops group. 4) Among 11 patients who were followed up more than 24 months, recurrent vertigo was substantially imporved by medical menagement in 7 patients and 4 patients had transmastoid labyrinthectomy to relieve vertigo. 5) Etiologic factors were viral infection in 62%, chronic otitis media in 18%, head trauma in 10%, febrile convulsion in 10%, congenital malformation in 2%, meningitis in 2%, and no contributing factors in 28% of patients.