OBJECTIVE AND IMPORTANCEWe describe a rare case of a ruptured distal anterior thalamoperforating artery aneurysm associated with right internal carotid artery occlusion.CLINICAL PRESENTATIONA 59-year-old woman experienced sudden occipital headache, vomiting, and subsequent coma as a result of massive intraventricular hemorrhage. An initial angiogram revealed only an occlusion of the right internal carotid artery just distal to the posterior communicating artery. Repeat angiography 1 month later, however, revealed a saccular aneurysm at a distal anterior thalamoperforating artery in addition to the occlusion of the internal carotid artery.INTERVENTIONWe approached this aneurysm through the right temporal horn after opening the ambient cistern. The aneurysm, which was located in the brain parenchyma just medial to the temporal horn, was successfully resected.CONCLUSIONThis rare aneurysm probably developed as a result of hemodynamic stress on the anterior thalamoperforating artery after occlusion of the internal carotid artery and/or secondary to chronic hypertension.