<p>Objective: Extracranial-intracranial direct anastomotic bypass is an established surgical treatment method for moyamoya disease in adults with an ischemic presentation. Although various procedures, including direct-indirect complex bypass, have been reported, the optimal method is yet to be elucidated. The purpose of this study was to clarify the usefulness of superficial temporal arterymiddle cerebral artery (STA-MCA) single anastomosis, which is the simplest mode of direct bypass surgery without an additional indirect procedure for ischemic moyamoya disease in adults.</p><p>Methods: Sixty-four hemispheres of 46 patients with adult-onset (≧16 years) ischemic moyamoya disease who underwent bypass surgery during the recent 3.7 years were analyzed. In all cases, STA-MCA single anastomosis was performed without additional indirect procedures. Perioperative complications, hemodynamic improvement in single-photon emission computed tomography findings (SPECT), extent of angiographic revascularization, and neurological events during the follow-up period (mean ± SD: 773 ± 380 days) were evaluated.</p><p>Results: Cerebral infarction and subdural/epidural hematoma were found in 2 (3.2%) and 3 (4.8%) cases, respectively, and 21 (33.9%) cases presented with transient neurological deficits presumably caused by local hyperperfusion. None of the cases showed neurological sequelae at discharge. The cerebral blood flow in the MCA territory showed significant elevation after surgery. In all cases, bypass patency was confirmed using angiography, and the extent of angiographic revascularization was more than two-thirds of the MCA territory in 56 (5%) of the cases and one-third to two-thirds in 38 (7%). The only neurological event that occurred during the follow-up periods was transient ischemic attack in 2 patients.</p><p>Conclusion: The present study provides reasonable grounds for choosing simple STA-MCA single anastomosis as the first choice of treatment for adult-onset ischemic moyamoya disease.</p>