A series of 16 patients with unilateral ophthalmoplegia due to mass lesions of the cavernous sinus was analyzed; there were six cavernous meninglomas and nine intracavernous aneurysms. All meningiomas were characterized by painless, insidiously progressive partial nerve palsies, as were half of the aneurysms; the remaining aneurysm patients experienced acute painful episodes. Pharmacologic pupillary tests failed to confirm a coexisting Horner syndrome in the majority of cases with anisocoria. Although plain skull films were unremarkable or misinterpreted as normal, bone tomograms, computerized axial tomograms, radionuclide scans, and cerebral angiograms established the diagnosis in all cases. Because cavernous meningiomas show slow progression and are surgically inaccessible, craniotomy is advised only if the visual pathways or brain stem is compromised. Intractable pain appears to be the only distinct indication for intervention with cavernous aneurysms.