Finding predictors of chronic graft-versus-host disease (cGVHD) in children would be extremely useful. Because of recent data suggesting that cGVHD may be a Th-2-mediated process, a theoretical foundation linking eosinophilia and cGVHD exists. While an association between eosinophilia and cGVHD has been described in adults, it has never been described in children. We studied 53 patients that received allogeneic hematopoietic stem cell transplants (SCT) between 1999 and 2002. Ten (19%) of these patients developed eosinophilia (absolute eosinophil count (AEC) > 500x 10/L) after day 100. Of these ten, eight either had or later developed cGVHD. We conclude that following the peripheral eosinophil count in children post-SCT is useful, and a rise in the AEC may herald the development of cGVHD. Taking the AEC into account with other risk factors (such as previous grade II-IV acute GVHD, human leukocyte antigen (HLA)-mismatch, and unrelated donor (URD) transplant) may improve our ability to predict cGVHD.