It has previously been shown that enteral nutrition has several advantages compared to parenteral nutrition (PN) in critically ill patients. The nutritional history was studied in 231 patients after allogeneic stem cell transplantation (SCT). Parenteral nutrition was given for a median of 10 (0-74) days. Patients with graft-versus-host disease (GVHD) grades III-IV received more PN (median 20, range 0-67) than patients with GVHD grades 0-II (10, 0-74, P=0.016). Eighty-five (37%) patients were not able to eat anything for a median of 4 days (1-37). We found a correlation between the number of days with no oral intake (before the diagnosis of acute GVHD) and the incidence of acute GVHD grades III-IV. In patients with 1-4 days of no oral intake, the incidence of grades III-IV acute GVHD was 6%, in those with 5-9 days it was 17%, and in those with >9 days it was 38%. On multivariate analysis, we found that more than 9 days with no oral intake was associated with acute GVHD grades III-IV (odds ratio 7.66, confidence interval 1.44-40.7, P=0.016). Poor oral intake early after SCT may be associated with an increased risk of developing severe acute GVHD.