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 times. Authors deal with the statistic analysis of operation method, causative organism and results on 209 cases, which were confirmed to cholesteatoma of middle ear and mastoid during the period of Jan. 1983 to Dec. 1987, and the following results were obtained : 1) The total cases of operation was 738, of which 209 cases(29.3%) were cholesteatomatous disease. 2) Sex ratio was 1.5 : 1, male predominance with 110 left and 99 right affected ears. 3) Age distribution showed 79 cases(38%) in 3rd decade, 71 cases(34%) in 2nd decade, 32 cases(15%) in 4th decade, 12 cases(6%) in 5th decade and the youngest patient was 5 years old and the oldest one was 65 years old. 4) The methods of operation were as follows : Canal wall down mastoidectomy with tympanoplasy was 145 cases(69%), radical mastoidectomy 29 cases(14%). Besides, modified radical mastoidectomy and intact canal wall mastoidectomy were done. 5) Postoperative follow up audiogram showed that loss of hearing(below 10 dB) was 59 cases(28%) and gain of hearing(below 10 dB) was 81 cases(39%). 6) The most common state of ossicles was the cases with no ossicles(42%) and the 2nd, stapes only(21%). 7) The most common preoperative temporal bone X-rays showed sclerotic type, 163 cases(78%) and the size of the durm perforation was variable. 8) On the preoperative pus culture, proteus mirabilis and pseudomonas aeruginosa were most common organisms and cepharosporin and aminoglycoside were most sensitive drugs.