The engraftment syndrome (ES) is a phenomenon observed in some patients undergoing autologous hematopoietic stem cell transplant (AHSCT). ES is characterized by fever, rash, capillary leak, and pulmonary infiltrates occurring at the onset of engraftment. Prior studies have suggested that the administration of hematopoietic growth factors post-transplant results in the increased frequency of ES. However, the relative contribution of granulocyte colony-stimulating factor (G-CSF) vs granulocyte-macrophage colony-stimulating factor (GM-CSF) to the development of ES remains unknown. A total of 152 consecutive patients who were treated with high-dose chemotherapy and AHSCT supported by either G-CSF or GM-CSF were analyzed retrospectively. In all, 20 patients developed ES, an incidence of 13%. ES was seen more frequently in patients who received GM-CSF (GM-CSF 24% vs G-CSF 4%, p=0.0001). The highest incidence of ES was observed in breast cancer patients (42% of breast cancer patients; 70% of all ES cases). Comparison of the incidence of ES by the priming regimen used comprising either of the growth factors revealed no significant association (p=0.8224). This study demonstrates that the incidence of ES is higher using GM-CSF, particularly in patients with breast cancer. It suggests that it might be advantageous to administer only G-CSF in breast cancer patients undergoing AHSCT to reduce ES-related morbidity.