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Background: The Japan Otology Society (JOS) proposed the classification and staging system for middle ear cholesteatoma. However, there was little analysis of the pathology of cholesteatoma using this staging system. Aims/objectives: To analyze the pathology of pars flaccida cholesteatoma using the staging system by JOS. Material and methods: A total of 183 cases of fresh pars flaccida cholesteatoma treated between January 2009 and December 2015 were included. We used the staging system recommended by JOS (2015). The association of the following variables in each stage of pars flaccida cholesteatoma was examined: age, gender, preoperative hearing level, staging, statuses of mastoid cell growth and stapes, tympanic sinus invasion. Results: Stage II disease showed the highest degree of progression, and peak incidence was observed in the third and fourth decades of life. Stage III significantly increased after the age of 40 years. The progression of the disease stage was significantly associated with deterioration of hearing level. Cholesteatoma invasion to tympanic sinus was recognized in 14.2% of cases. The state of the stapes is increasingly likely be to fracture as stage progresses. Conclusions: The JOS Staging System appropriately reflects the disease state, and it was found to be clinically meaningful in this study. [ABSTRACT FROM AUTHOR]