Reduced mastoid pneumatization is common in childhood otitis media with effusion(OME) and there is controversy whether reduced pneumatization may result from or in OME. However, mastoid pneumatization improves after medical therapy and ventilation tube, and changes in pneumatization are important to predict the prognosis. The purpose of this study was 1) to evaluate the middle ear and mastoid pneumatization by temporal bone CT compared to the prognosis, 2) to establish the treatment regimen. We evaluated temporal bone CT in nine childhood OME patients(18 ears) who had a history of ventilation tube insertion one time or more and we compared temporal bone CT findings with prognosis. Results were as follows : 1) Seven ears that had good pneumatization recovered to normal. 2) Six ears among 11 recurrent ears showed slightly decreased pneumatization with hazziness and air density in antrum. Five ears recovered after medical treatment, but one ear which did not respond to medical treatment was treated with ventilation tube. 3) Five ears among 11 recurrent ears showed markedly decreased pneumatization with sclerosis or underdevelopment and soft tissuedensity in antrum. In two ears, scutum was eroded. Not all responded to medical treatment so that four ears were treated by ventilation tube again and one ear was treated by mastoidectomy and tympanoplasty. In conclusion, it is important to observe the mastoid pneumatization and middle ear by temporal bone CT in the decision of treatment plan and in consideration of prognosis.