Fifty-five patients with osteogenesis imperfecta (01) were studied to determine the extent to which the peripheral auditory mechanisms share in the connective tissue lesion. Ninety-two unaffected relatives and 43 control subjects were also studied. Subjects were divided into age groups younger than and older than 30 years. Hearing loss, most frequently sensorineural, occurred in 49% (younger than 30 years) and 94% (older than 30 years) of patients with 01. A sensorineural pattern of hearing loss, here considered characteristic of 01, was observed in 47% of 01 subjects irrespective of age, in 42% of relatives, and 5% of controls. Middle ear analysis by tympanometry and acoustic reflex analysis indicates that, although some patients with 01 have a stiff middle ear system similar to that seen in otosclerosis, the majority display absent acoustic reflexes and increased compliance of the middle ear with notched tympanograms suggestive of anomalous ossicular articulation. Similar findings in otherwise uninvolved relatives suggest a genetic basis for these defects.