Since 1967. we have performed microsurgery of middle ear and mastoid to the patients of chronic ear disease and reported its methods and results on several occasions. This paper deals with the statistic analysis of the procedures and results on 473 cases, which were confirmed to cholesteatoma of middle ear and mastoid, during the period of May. 1967 to June, 1979. 1) The total cases of operation were 473 : 261 cases (55%) were male and 212 cases (45%) were female. Sex retio was 1.2 : 1. 2) Age distribution shows 213 cases (45.0%) in 2nd decade, 142 cases (30.0%) in 3rd decade, 49 cases (10.4%) in 1st decade and the youngest patient was 2 yrs old and the oldest one was 64 yrs old. 3) The result of operation : Complication of radical mastoidectomy was 35 cases (15.6%) among 224 cases, that of modified radical mastoidectomy or 2-chamber style tympanoplasty was 10 cases (25.6%) among 39 cases and that of intact canal wall typanoplasty with mastoidectomy was 72 cases (34.3%) among 210 cases. Therefore, 117 cases (24.7%) of total operation revealed postoperative complications. 4) The analysis of postoperative complication : Postoperative infection was 60 cases (13%), recurred cholesteatoma was 53 cases (11%), others 4 cases (1%).