Anatomical and biological studies of cavernous sinus meningiomas help us understand the biological heterogeneity of these tumors. The question of whether cavernous sinus meningiomas infiltrate cranial nerves is clinically important because of the effect on treatment planning. In the authors' experience of treating 36 patients with cavernous sinus meningiomas, tumor invasion into a cranial nerve was documented in two patients in whom a cranial nerve was resected during the cavernous sinus dissection. In both patients, histological examination using hematoxylin and eosin and bodian stains showed infiltration of the cranial nerves by a benign meningioma which, to the best of the authors' knowledge, is a condition previously unreported. This histological finding of meningioma invasion into a cranial nerve demonstrates the biological heterogeneity of cavernous sinus meningiomas and raises concern about the invasive character of meningioma. Because not all tumor cells can be identified radiologically or by direct visualization at surgery, occult tumor infiltration predisposes a patient to recurrence despite the best neurosurgical efforts. Evidence of cranial nerve infiltration by meningioma suggests that, in some circumstances, cavernous sinus dissection in the hope of total removal of a meningioma may be futile and, in the long term, may provide no advantage over treatment options with lower morbidity.