Encephalo-duro-arterio-synangiosis (EDAS) is a relatively new surgical procedure ofr treatment of childhood moyamoya disease. We assessed regional cerebral perfusion in moyamoya patients efore (1.3 mo) and after (6.8 mo) EDAS with 99mTc-HMPAO brain SPECT. A total of 21 EDAS operations in 17 moyamoya patients was included. Preoperative CT or MRI showed cerebral infarction in 14 patients and carotid angiography showed Suzuki grade 1 to V stenosis in 6%, 9%,62%,12% and 12% of the hemispheres respectively. Preoperative SPECT showed regional hypoperfusion in all patients, bilateral frontal and temporal loves being the most frequently involved site. 4*4 pixel sezed ROIs were applied on the frontotemmporal cortex in 3 slice averaged transverse tomographic images. An index of regional perfusion was measured as; PI (%)= average FT activity/average cerebellar activity*100 Pre-EDAS ipsilateral PI ranged from 23.7 to 98.4% (mean:74.3 +- 17%) and increased significantly after operation (81.4 +- 17%, p<0.001). Individual post-EDAS PI improved in 15/21 cases, showed no significant change in 5 and was slightly aggravated in 1. The amount of clinical improvement ( CI) was graded with a scale of 0 to 4 based on frequency and severity of TIA attacks. When patients were grouped according to pre-EDAS PI, group II (PI 70~89) showed a significantly higher CI (3.3) compared to group I (PI<70, 1.57) of group III (PI>90, 0.5) (p<0.001). The amount of perfusion improvement ( PI) showed signifiant correlation with CI (r-0.42, p=0.04). PI did not, however, correlate with the amount of neovascularization assessed angiographically in 8 patiets. Serial HMPAO SPECT is an useful noninvasive study ofr assessing perfusion improvement after EDAS in childhood moyamoya patients.