Using a fine, rigid endoscope (Olympus, SES-1711K), we examined the middle ear, including the tympanic orifice of the eustachian tube, of children with otitis media with effusion (OME) in its active stage (26 ears), in the convalescent stage (13 ears), and during treatment with ventilation tubes for 10 days to 6 months (five ears) through myringotomy with the patients under general anesthesia. Several color photographs of representative ears are shown. In the active stage of OME, edema (73.1%) and hyperemia (23.1%) were characteristic features of the middle ear mucosa, and normal mucosa was seen in only one ear (3.1%). The tympanic orifice of the eustachian tube, which could be examined in 12 ears, were stenosed with edema in four ears (33.3%) or plugged with effusion in three ears (25.0%) in this group. In the convalescent stage of OME, dilated vessels were most often seen (69.2%), but the rest of the patients had normal mucosa (30.8%) in the middle ear, and none of them had edema nor hyperemia. The tympanic orifice of the eustachian tube, which could be examined in five ears, was clearly patent in all the patients in this group. One ear that was treated with a ventilation tube for 1 month showed dilated vessels and less severe inflammation than did ears that were in the active stage of OME, and three ears that were treated for more than 3 months showed almost normal middle ear mucosa.