To evaluate the significance of clinical abnormalities occurring during the peri-engraftment period following allogeneic hematopoietic cell transplantation (HCT), we retrospectively analyzed the data of 216 allogeneic HCT recipients. The most frequently observed peri-engraftment clinical abnormality (PECA) was noninfectious fever in 58 patients, followed by hepatic dysfunction in 39, weight gain in 22, and renal insufficiency in 11. Frequently identified predictive factors for a higher incidence of each PECA were HCT from an unrelated or mismatched donor, GVHD prophylaxis with cyclosporine alone, and rapid engraftment. Considering that donor type and GVHD prophylaxis are closely related to GVHD, these observations suggest that the development of PECAs might be associated with a graft-versus-host reaction. This hypothesis was supported by the fact that the patient group with each PECA showed a higher incidence of grades 3-4 acute or chronic extensive GVHD, with varying degrees of statistical significance. Although our data should be interpreted cautiously in view of their retrospective nature, some of the PECAs occurring after allogeneic HCT may be atypical manifestations of GVHD and may be associated with severe forms of acute or chronic GVHD.