It is important to realize that not all intracanalicular filling defects observed during myelography of the internal auditory meati are due to tumors. In order to minimize the possibility of diagnostic errors one should be aware of: (1) the relationship between the size of the internal auditory canal and the capacity of the subarachnoid space within the canal; and (2) the size and course of the neurovascular structures within the meatus. Certain rules in the technique of the examination and diagnostic criteria are outlined which should be followed in all cases with questionable intracanalicular filling defects.