Despite the high incidence and prevalence of otitis media, its pathogenesis is not thoroughly understood. In an effort to provide a better understanding of this disease, experimental animal models have been developed which corroborate the changes observed in humans. In this study a new factor was added: tympanic membrane perforation 1 week after Eustachian tube obstruction. Twelve cats were divided in 4 even groups, and sacrificed at 1 and 2 weeks, 1 and 3 months after perforation, and their temporal bones were studied. Findings revealed an early massive reaction of the mucoperiosteum with granulation and polypoidal tissue formation which filled a considerable portion of the middle ear cavity. Polypoidal changes involved the stapediovestibular joint, possibly explaining the cases of stapes fixation found at tympanomastoidectomy procedures for chronic otitis media. Cholesterol granulomas with the classic characteristics as described in humans were observed in all animals at 3 month periods. These were preceded by clefts in the effusions, at 1 month, containing red blood cells. These clefts were considered as probable precursors of cholesterol granuloma formation. The association of endolymphatic hydrops, round window membrane changes, and otitis media without purulent labyrinthitis was observed; however, it was felt that the paucity of animals precluded any definite conclusions.