Clinical otological features, hearing status and middle ear function in 201 patients with osteogenesis imperfecta are presented. The study covered 76% of the expected total number of patients with osteogenesis imperfecta in Denmark. 78% of the patients exhibited an autosomal dominant inheritance pattern with an almost 100% penetrance. In 39% of the ears examined, a conductive or mixed hearing loss was found. Sensorineural hearing loss or anacusis was seen in 11% of the ears. In most cases the onset of hearing impairment was noted in the second or third decade and progressing with increasing age, especially after the age of 60. Tympanometry and acoustic reflex measurements suggested that the cause of conductive or mixed hearing loss was stapedial fixation and in a few cases ossicular discontinuity due to aplasia or fracture of the stapedial crura. Findings during stapedectomy in 32 patients confirmed these assumptions.