We have performed microsurgery for 189 cases of patients with middle ear and mastoid diseases during the period of Jan. 1982 to Dec. 1984. In this investigation, author analyzed 189 cases of chronic otitis media clinicostatistically. And the following results were obtained. 1) The total cases of operation were 189, 105 cases were male and 84 cases were female(male-55.6%, female-44.4%). 2) Age distribution shows 35 cases(18.5%) in 2nd decade, 98 cases(51.9%) in 3rd decade. 3) Site incidence of operated cases ; Rt. side was 97 cases(51.3%) Lt. side was 92 cases(48.7%). 4) Duration of disease ; less than 1yr was 45 cases(23.8%), over 10yr was 79 cases(41.8%). 5) Chief complaint ; Otorrhea was 140 cases(46.8%), hearing difficulty was 87 cases(29%). 6) Character of otorrhea ; Mucopurulent state was 80 cases(57.1%) mucinous state was 49 cases(35%), serous state was 11 cases(7.9%). 7) Site of drum perforation ; 109 cases(57.7%) in central perforation, 20 cases(10.6%) in total perforation, 35 cases(18.5%) in attic, 17 cases(9%) in marginal perforation, 8 cases(4.2%) in adhesion. 8) Condition of Eustachian tube function ; Good state was 152 cases(80.4%). Stenotic state was 9 cases(4.8%) and obstructed state was 28 cases(14.8%). 9) X-ray findings of temporal bone were sclerotic type in 137 cases(72.5%) diploic type in 41 cases(21.7%) pneumatic type in 11 cases(5.8%). 10) Types of preoperative hearing loss ; conductive type in 68 cases(36.%) sensorineural type in 28 cases(14.8%) normal in 62 cases(32.8%). 11) Conditions of middle ear mucosa ; unhealthy in 135 cases(71.4%) healthy in 54 cases(28.6%). 12) Conditions of ossicle ; Intact state in 69 cases(36.5%), destructed state in 120 cases(63.5%). 13) The route of approach was endaural in 46 cases(24.3%) postauricular in 141 cases(74.6%) transmeatal in 2 cases(1.1%). 14) Type of anesthesia ; 164 cases(86.8%) by general anesthesia, 25 cases(13.2%) by local anesthesia. 15) Graft materials for the perforated drum were temporalis muscle fascia in 136 cases(91.9%). 16) Postoperative complications were persistent discharge in 7 cases(3.7%), perforation in 5 cases(2.6%) and 5 cases(2.6%) were wound infection. 17) Type of operation ; Tympanomastoidectomy with tympanoplasty(ICW) : -39 cases(20.6%), Tympanomastoidectomy with tympanoplasty(open cavity) : -83 cases(43.9%), Tympanoplasty : -25 cases(13.3%), Radical mastoidectomy : -18 cases(9.5%), Simple mastoidectomy : -11 cases(5.8%), Modified radical mastoidectomy : -9 cases(4.8%), Atticotomy and tympanoplasty : -2 cases(1%), Tympanotomy : -2 cases(1%).