During a period of six years, eleven cases, (involving sixteen ears), of osteomyelitis temporalis chronica (otitis media in the broad sense) with cholesterin granuloma, accompanied by experimented studies of cholesterin granuloma in the tympanic cavity of rabbits were reported. Cholesterin granuloma appeared in the tympanic cavity of the rabbits after instilation of a 1 solution of oxalic acid in the tympanic cavity. Cause of the appearance of cholesterin crystals was fatty degeneration due to disturbances of the blood stream. In many cases cholesterin granuloma appears in the marginal portion of the mastoid cells far from the antrum. Histopathologically, this appears of the mucous membrane of the mastoid cells, and sometimes in the osteomyelitic tissue. In only two cases was this found in the aditus ad antrum or epitympanic cavity. Diagnosis : Microscopical evidence of cholesterin crystals in the pus in the tympanic cavity obtained by punction, or in the mastoid cells obtained by mastoid operation. Histological evidence of cholesterin granuloma in tissues of several parts of mastoid cells obtained by operation. Yellowish, bluish or black ear drum especially in children must be given immediate attention. rtant. In every case, these showed up cloudy, or osteomyelitic. Hard of hearing in these cases is as follows : in mild cases, it appears as conductive deafness. In medium cases, it was of mixed type, and in severe cases, patients were both deaf and dumb. Care must be taken, as there were three children both deaf and dumb in eleven patients observed. Therapy : Diagnosis and operation are most important in the early stages to prevent deafness. In these operations, mastoid cells, involved bony tissues, and cholestirin granuloma tissues must be removed completely.