Summary:We prospectively analyzed the incidence, risk factors and outcome of engraftment syndrome (ES) in 112 patients undergoing autologous peripheral blood progenitor cell transplantation with different malignancies between January 1999 and December 2003. The median age was 8 years (range 1-18). There were 73 males. There were 37 hematological neoplasias and 75 solid tumors. Disease status at transplantation was early in 49, intermediate in 15 and 48 in advanced phase. The median CD34 þ cells infused was 4.6 Â 10 6 /kg. With a median follow-up of 23 months (1-116 months), 38 patients developed ES. The cumulative incidence of ES was 34.574.5% and the event-free survival was 58.3712%. There were no differences in the causes of death between patients with or without ES. A high number of CD34 þ cells/kg infused, patients transplanted in early phase, the type of malignancy (solid tumor) and conditioning regimens other than busulfan based were significantly associated with ES in a multivariate analysis.