Age, hematopoietic growth factors, cyclosporin A, mode of bone marrow transplantation (BMT) (autologous, allogeneic-related, unrelated), and underlying disease were assessed as potential risk factors for capillary leakage syndrome (CLS) in 96 patients after BMT. CLS was defined as unexplained weight gain of > 3% within 24 h and nonresponsiveness to furosemide. CLS occurred in 9/21 patients after unrelated compared with 2/33 after allogeneic-related BMT (p = 0.0017) for hematopoietic disorders (n = 54) and in 6/7 patients after allogeneic-related compared with 3/35 after autologous BMT (p = 0.001) for solid tumors (n = 42). Hematopoietic growth factors and cyclosporin A were no significant risk factors on their own. We conclude that unrelated BMTs or high-intensity conditioning regimens used in combination with allogeneic-related BMT are the main risk factors for CLS.