AbstractBehçet's disease (BD) is a relapsing systemic inflammatory disorder of unknown etiology involving systemic vasculitis. Vasculitis in BD results from the involvement of arteries, veins and blood vessels of all sizes, which leads to the three major manifestations of this condition: venous occlusion, arterial occlusion and aneurysm formation. Therefore, whole‐body vascular involvement should always be considered in BD patients. Here, we describe the first appearance of an internal carotid‐posterior communicating artery aneurysm, resulting in complete oculomotor nerve palsy in a BD patient. A 44‐year‐old Japanese man suffered from recurrent episodes of erythema nodosum that had presented on the lower extremities for the past 2 years. His condition was diagnosed as an incomplete type of BD based on relapsing oral and genital ulcers, skin eruptions, such as erythema nodosum and folliculitis, a positive pathergy test and systemic arthralgia. Ten years after his initial clinical presentation, he had manifestations of right‐sided ptosis and cyclic dull pain in his right temporal region. Magnetic resonance imaging and angiography revealed a right internal carotid artery‐posterior communicating artery aneurysm. Although oculomotor nerve palsy associated with internal carotid artery‐posterior communicating artery aneurysm in a BD patient has not been reported previously, our report highlights the fact that this abnormal manifestation should be considered in those with vasculo‐BD.