Microfractures of the temporal bone have been recognized for more than seventy years and occur in certain well-defined areas of the otic capsule. The etiology and significance of these microfractures has been debated since their discovery. The most commonly held theory is that they result from stresses within the otic capsule that develop with growth. An alternative explanation might be that they result from masticatory stress placed upon the temporal bone. Fifty serially-sectioned temporal bones from the Ontario Temporal Bone Bank were examined in this study for the presence of microfractures. Our findings as to the most common sites of microfractures agree with previous studies. It is proposed that the constant stress placed upon the petrous temporal bone by the act of mastication is directed by the anatomy of the external, middle and inner ear through certain definite pathways, including the Fallopian canal, the bony semicircular canals and the cochlea. The most common sites of these fractures represent sites of weakness in the path of these directed forces within the otic capsule, and the statistically significant increase in the number of fractures with age lends support to the masticatory stress theory.