The current study defines the incidence and clinical manifestations of hyperacute graft-versus-host disease (haGVHD; fever, skin rash, diarrhea, and hepatic dysfunction) and analyzes the risk factor and the impact of haGVHD on the results of allogeneic stem cell transplantation (SCT). In all, 90 patients underwent allogeneic SCT from 71 matched siblings or 19 alternative donors. Immediate high-dose steroids were administered to 22 patients who met the criteria. The overall incidence of haGVHD was 36.7% (n=34) and haGVHD was also strongly correlated with acute (aGVHD) (P<0.001) and extensive chronic GVHD (cGVHD) (P=0.007), and found to be associated with decreased probability of relapse (P=0.0017). Early intervention with steroids within 7 days after the diagnosis of haGVHD might be associated with better survival. A survival analysis of the overall survival and disease-free survival did not reveal any difference between haGVHD+ and haGVHD- groups. In multivariate analysis, the use of an alternative donor (P=0.020) was identified as the only risk factor. Immediate high-dose steroids were effective in treating haGVHD. We conclude that in an allogeneic setting, haGVHD is not an uncommon manifestation, associated with the development of aGVHD or cGVHD. The only risk factor for haGVHD was the use of an alternative donor.