Purpose: Parenteral nutrition (PN) is a standard supportive care for pediatric patients undergoing hematopoietic stem cell transplantation (HSCT) in Samsung Medical Center. The objective of this study was to identify the factors associated with the length of hospital stay (LOS) in pediatric HSCT patients administrating PN routinely. Methods: This was a retrospective study for 128 pediatric HSCT patients from Aug. 2008 to Dec. 2009. Demographics, nutrition status on the first report in the nutrition support team, calories and nutrients supplied, PN duration, LOS, PN-induced complications, and laboratory data were collected from electronic medical records. Multivariate analyses were conducted to identify factors associated with LOS. Results: The median age of registered patients was 70 months (range 6∼239 months). Twenty-three patients (18.0%) were malnourished moderately to severely when PN was started. Number of autologous HSCT was larger than allogeneic HSCT (87 vs 41). In children undergoing HSCT, LOS was significantly correlated with PN duration (P＜0.001) and graft type (P＜0.001). Especially, in autologous peripheral blood stem cell transplantation (PBSCT), malnourished patients at the beginning of PN were shown the tendency to increase LOS (P=0.024) and PN duration (P=0.043). Conclusion: In pediatric HSCT patients administrating PN routinely, LOS was associated with a graft type of HSCT and PN duration. Especially for autologous PBSCT patients, the nutrition status at the beginning of PN had the influence on LOS and PN duration. During the peri-HSCT period, careful nutrition monitoring can prevent malnutrition, decrease PN duration, and shorten LOS. (JKSPEN 2011;4(1):1-6)