Six patients who experienced transient neurological deteriorations with no evidences of hemorrhage and infarction after encephaloduroarteriogaleosynangiosis for moyamoya disease were evaluated with semiquantitative analysis using brain perfusion SPECT. Postoperative transient neurological deteriorations topographically corresponded to hyperperfusion areas on SPECT. Cerebral blood flows of both the operated hemisphere and focal hyperperfusion area increased significantly after surgery (P=0.046 and 0.028, respectively), compared with the preoperative ones. Symptomatic cerebral hyperperfusion may occur transiently after indirect revascularization surgery for adult moyamoya disease. Further study is needed to clarify the exact mechanism of cerebral hyperperfusion after indirect surgery.