The association of sinusitis with ocular motility disorders is a seductive theory due to their close anatomical vicinity. Typically, sinusitis can influence ocular motility by affecting single muscles or a combination of muscles and/or cranial nerves due to a local inflammatory tissue reaction. Although rare, sinusitis has been suggested at least as a cause for superior-branch oculomotor palsy. We report a case of progressive, isolated, third-cranial-nerve palsy caused by an aneurysm of the posterior-communicating artery that initially was thought to be related to pansinusitis.