The pneumatisation of the temporal bone after mastoidectoniy in early childhood was checked by X-ray examination in 79 cases. The younger the children have been at the time of the operation, the higher was the percentage of a new good pneumatisation of the temporal bone in the later age. A characteristic finding was a difference in the size of the cells, even if the pneumatisation has developed good again. The statistic evaluation showed, that the application of antibiotics had no significant influence on pneumatisation. In addition there was no connection between finding’s at the time of operation, duration of healing, results of the bacteriological examination and pneumatisation. On the contrary years later all cases with recurrent mastoiditis developed a sclerotic mastoid. The swabs of the auditory cannal showed much more staphylococci, than out of the mastoid cavity. In the mastoid cavity the streptococci were the most seen germs. As a result of the audiomelric examination patients with sclerotic mastoids after mastoidectoniy in childhood had a higher percentage of hearing loss, than those with a good pneumatisatio