In 1969, Okayama Kanariya Gakuen was established as the first auditory training nursery for hard-of-hearing preschool children in Japan. From April, 1969 through March, 1980, 541 among the 1,400 children consulted there, were diagnosed as having bilateral sensorineural hearing impairment. The etiology of the impairments were classified as congenital, prenatal, perinatal or acquired. Seventy-three of the 541 cases (13.5%) were of genetic etiology. Their parents and/or brothers were diagnosed as having sensorineural hearing impairment during childhood, too. Ninety cases (16.6%) were due to maternal or prenatal disorders. Twenty-two of these cases were affected by maternal rubella. Two hundred nineteen cases (40.5%) suffered from perinatal disorders. It was suggested that anoxia was an important factor causing hearing impairment. One hundred forty-seven cases (27.2%) were due to acquired diseases which might cause hearing impairment. No abnormalities in family or past history were found in 182 cases (33.6%). This study seemed to have an advantage in that the subjects were relatively young and, therefore, detailed and reliable historys could be taken. The etiology of many other cases, however, still remains unknown even though they apparently had abnormalities in family and/or past historys.