Eight children underwent reduced-intensity stem cell transplantation (RIST) from an HLA-matched sibling. They received a fludarabine-melphalan based preparative regimen. Stem cell source was bone marrow, and GVHD prophylaxis consisted of cyclosporine A alone. Acute GVHD grade II-IV and grade III-IV were observed in four (50%) and three (37.5%), respectively, out of these eight patients. This incidence was significantly higher than that after conventional bone marrow transplantation, without severe tissue damage, in the same setting of stem cell source and GVHD prophylaxis. Although the number of patients is small, our results suggest that incidence of acute GVHD after RIST for children is significant. It should be remembered that RIST for children does not seem to be an easy transplant procedure from the viewpoint of acute GVHD, although RIST is less toxic.