Objectives: We evaluated the incidence of facial canal dehiscence in patients with chronic otitis media with or without cholesteatoma, adhesive otitis and tympanosclerosis who underwent canal wall-down tympanomastoidectomy or canal wall-up

cholesteatoma, adhesive otitis and tympanosclerosis who underwent canal wall-down tympanomastoidectomy or canal wall-up tympanomastoidectomy. Materials and Methods: We performed a retrospective study in a tertiary referral hospital of operated 228 patients between April 2008 and June 2013. Using intraoperative findings, data were collected regarding the patients’ age upon presentation, gender, clinical diagnosis, presence of cholesteatoma, preopeartive and postoperative facial nerve function, presence or absence of facial canal dehiscence and its location, lateral semicircular canal fistula or dural exposure due to erosion of bony plate. Results: The frequency of facial canal dehiscence in our patients was 28.1%. The most common site of dehiscence (68/228, 82.8%) was the tympanic segment (P<0.001) and the incidence of facial canal dehiscence in ears with cholesteatoma (92.2%) was distinctly higher than than other ears (P < 0.001). When the pediatric group (≤16 years of age) and the adult group (>16 years of age) were compared, 10.5% of the 38 pediatric age patients had facial canal dehiscence, while 31.6% of the 190 adult patients (P<0.05). The most common accompanying findings were respectively dural exposure (12.7%) and lateral semicircular canal fistula (11%). There was a statistically significant correlation between semisircular canal fistula and dehiscence (P<0.001) and in the ears with dural exposure and dehiscence (P<0.01). The dehiscence was was seen significantly more often in patients who had the canal wall-down tympanomastoidectomy than in those who had the canal wall-up tympanomastoidectomy (P<0.001). The incidence of dehiscence was more often in female patients and in primary surgery group but both results were not statistically significant. Conclusions: Dehiscence of facial canal was mostly seen in patients with cholesteatoma and mostly located in the tympanic segment. Also, most common site for the facial nerve injury during otologic surgery is the tympanic segment and mechanical dissection is most often indicated in this region. The presence of semicircular canal fistula and dural exposure on preoperative computerized tomography of temporal region are invaluable clue for presence of dehiscence.