A case of atrial myxoma with cerebral oncotic aneurysms was presented. A 37 year-old woman was admitted complaining of right hemiparesis, and episodes of syncope. Neurological examination on admission revealed a right arm monoparesis, a right hemisensory disturbance, and a motor aphasia. Computed tomography (CT) demonstrated low density areas in the left fronto-parietal region, and multiple discrete enhancing high density spots scattered bilaterally in the parietal lobes. Cerebral angiography showed multiple fusiform peripheral aneurysms especially in the distribution of the bilateral middle cerebral arteries. Cerebral emboli from the cardiac source were suspected, and an echocardiography was performed, which disclosed a huge villous mass in the left atrium. The cardiac mass was resected uneventfully under cardiopulmonary bypass. It proved to be a left atrial myxoma. Postoperatively, her neurological deficit persisted. After the resection of the cardiac tumor, follow-up angiographies were undertaken twice. The second angiography performed 6 months later revealed spontaneous resolution or stabilization of most of the aneurysms detected before. On the other hand, newly-developed aneurysms were seen at the sites which had seemed normal previously on the first angiography. No remarkable changes were seen on the third one except the slight enlargement of one of the aneurysms in the middle cerebral territory. At 3 years she was neurologically stable. Because of the paucity of knowledge concerning the natural history of cerebral oncotic aneurysms and lack of definite treatment for them, long-term follow-up including serial angiography is mandatory after the resection of left atrial myxoma.