Thrombocytopenia (TP) is a frequent complication after allogeneic stem cell transplantation (SCT) and regarded as a poor prognostic factor, especially in patients with chronic graft-versus-host disease (GVHD), although various factors were related to the development of TP after allogeneic SCT. Sixty-three patients receiving allogeneic peripheral blood stem cell transplantation (PBSCT) were stratified according to platelet count (PC) at day +60 and analyzed in terms of overall survival (OS) and the incidence of non-relapse mortality (NRM). Ten patients (15.9%) were stratified in group 1 (PC </= 29 x 10(9)/L), 23 patients (36.5%) in group 2 (PC 30-79 x 10(9)/L), and 30 patients in group 3 (PC >/= 80 x 10(9)/L). Group 3 was associated with lower incidence of extensive chronic GVHD (p=0.013), better 3-yr OS (p=0.0030), and lower NRM rate (p<0.0001). In multivariate analyses, the PC at day +60 was identified as an independent prognostic factor (p=0.003) together with CD34+ cell dose (p<0.001), disease risk (p=0.004), and acute GVHD (p=0.033) in terms of NRM, and the PC (p=0.047) and CD34+ cell dose (p=0.026) in terms of incidence of infectious events. Measuring the platelet count at day +60 is a simple method for predicting the risk of chronic GVHD development and prognosis after allogeneic PBSCT.