IntroductionMoyamoya disease (MMD) is a chronic and progressive cerebrovascular occlusive disease involving the end of the internal carotid artery (ICA) and the main branches within the circle of Willis (COW) [1, 2]. In Korea and Japan, more than half of the adult patients with MMD present with hemorrhagic stroke [2, 3]. The risk of recurrent hemorrhage in MMD is estimated at 11%-25% within five years and 19%-36% within ten years, with each subsequent hemorrhage increasing the risk of poor neurological outcomes [4]. The incidence of MMD-associated aneurysms is estimated to be 3%-14%, although the frequency of aneurysmal rupture as the cause of hemorrhagic MMD remains uncertain [5, 6]. MMD-associated aneurysms can be classified as peripheral aneurysms, which originate from collateral vessels, or saccular aneurysms, which originate from major intracranial arteries [7].The treatment strategies for MMD-associated peripheral aneurysms remain controversial because of their deep location, tortuosity, and fragility [7]. Peripheral aneurysms originate mainly from the lenticulostriate artery, thalamic perforating artery, or choroidal arteries [8]. Previous reports have described aneurysms treated with close observation, direct clipping, endovascular coiling, or direct revascularization [6].Herein, we report the case of a patient with Moyamoya disease that rapidly developed an MMD-associated pseudoaneurysm after direct revascularization. The patient recovered after endovascular coiling, and secondary revascularization was performed.