Vertical and horizontal measurements were made of the widths of the internal auditory canals of 435 histologically prepared temporal bones. The mean vertical width, measured at the porus acusticus, was 3.68 mm (range 2.10 to 5.26 mm), and the mean horizontal width, measured in the middle region of the canal, was 3.72 mm (range 2 to 5.8 mm). The 144 ears selected for study because they exhibited slowly progressive sensorineural hearing loss showed a distribution of canal widths similar to that of the group as a whole. Histological examination of the internal auditory canals failed to show any type of soft tissue lesion which might have contributed to narrowing of the canals. The study provides no anatomical or histological evidence for the existence of a small internal auditory canal syndrome.