The role of EC-IC bypass surgery has become a very controversial issue recently. EC-IC anastomosis was performed in 132 patients of stroke in our institute. Thirty six of them which could be followed up completely had a completed stroke and ten of these showed a significant clinical improvement by the next day of surgery. We studied the angiograms, CT scans and dynamic CT studies of all 36 patients to determine the common factors responsible for a significant clinical improvement in these ten patients. It was found that patients with occlusion of middle cerebral arteries and with good collateral circulation fared better than those with other lesions and good cross circulation. Site of low density on CT revealed patient with watershed low density did well. Characteristic of low density area was found to be a significant factors. If the low density area was homogeneous and well defined in an arterial territory, it was invariably associated with no improvement after surgery. Patients showing an improvement had scattered or irregular low density areas. Dynamic CT studies were not found to be significant.