Background Intra-cerebral hemorrhage (ICH) is a devastating complication that can result from superficial temporal artery-middle cerebral artery (STA-MCA) bypass in patients undergoing treatment for steno-occlusive cerebrovascular disease (CVD).There is a clinical need to find the possible risk factors to prevent ICH,as it is a significant cause of mortality and morbidity.The aim of the study was to investigate the factors associated with delayed ICH after STA-MCA bypass in patients with steno-occlusive CVDs.Methods We retrospectively analyzed the records of 163 patients seen from 2002 to 2011 with STA-MCA bypass for steno-occlusive cerebrovascular diseases at the Department of Neurosurgery,Xuan Wu Hospital,Beijing.Demographic and clinical data,including age,gender,vascular risk factors,preoperative syndrome,preoperative National Institutes of Health Stroke Scale (NIHSS),ipsilateral ischemic lesions,classification of steno-occlusive CVDs,donor branches of STA,graft patency,postoperative hypertension,and postoperative-increased MCA velocity were recorded and analyzed.Binary Logistic regression served to identify factors associated with delayed ICH after STA-MCA bypass.Results We identified 8 (4.9％) patients with delayed ICH after STA-MCA bypass.Patients with hypertension,preoperative stroke,ipsilateral ischemic lesions,postoperative hypertension and postoperative-increased MCA velocity were significantly more prone to experiencing delayed ICH after STA-MCA bypass.Logistic regression analysis shows ipsilateral ischemic lesions,postoperative hypertension,and postoperative-increased MCA velocity remained independent predictors for delayed ICH after STA-MCA bypass.Conclusion Despite the varied associated factors in patients with steno-occlusive CVDs,ipsilateral ischemic lesions,postoperative hypertension,and postoperative-increased MCA velocity could be associated with delayed ICH after STAMCA bypass.