The dehiscences of the facial canal may be observed in any portion of the facial nerve ; the majority of gaps, however, are observed along the tympanic segment. They are located most frequently above and posterior to the oval window. Authors examined 138 human temporal bones(67 pairs and 4 unilateral temporal bones) from 71 persons by histologic examination of serially sectioned temporal bones. The results were as follows ; 1) Incidence of the facial canal dehiscences was 66.7% (92 dehiscences from 138 human temporal bones). Among these dehiscences, fifty seven cases(62%) revealed single dehiscence lesion and thirty five cases (38.0%) revealed multiple dehiscences lesions. 2) There were 36 bilateral dehiscences (65.5%) and 19 unilateral dehiscences (34.5%) among the 55 pairs of the temporal bones that could be observed facial canal dehiscences. 3) As the location of the dehiscences, one hundred three cases (80.5%) were located in the tympanic segment and 23 cases (18.0%) in the mastoid segment. Of all the dehiscences, sixty two cases (48.4%) were located adjacent to the oval window. In 2 cases (1.6%) of the temporal bones, dehiscences involved the entire length of the tympanic and mastoid segments.