Background: Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) represents a devastating complication observed in critical care medicine. The purpose of this study is to investigate the epidemiological aspects of ALI/ARDS in pediatric intensive care unit (PICU) and risk factors of mortality. Methods: Patients with ALI/ARDS in PICU of Beijing Children's Hospital, a tertiary medical center from November 1, 2005 to October 31, 2006 were included in this prospective study. We identified the risk factors for underlying diseases and mortality during a 3-month follow-up using multivariate logistic regression analysis. Results: In 562 critically ill patients admitted to PICU of Beijing Children's Hospital, there were 15 ALI-non ARDS patients and 29 ARDS patients, resulting in an incidence of 7.8% (44/562). The mortality rate of ARDS was 24.1% (7/29) and that of ALI/ARDS was 18.2% (8/44). At a 3-month follow-up, 12 patients died after being discharged from PICU and the total mortality rate was 45.5% (20/44). ALI/ARDS patients with pulmonary disease had better outcomes than those with extra-pulmonary involvements (P<0.05). Discharge against medical advice, low PaO2/FiO(2) during hospital stay and high PaCO2 on PICU admission were risk factors of mortality. Conclusions: ARDS has a high mortality rate in PICU, especially in those with extra-pulmonary diseases. In addition to aggressive medical management of comorbidity, lung protection and avoidance of discharge against medical advice will decrease the mortality. World J Pediatr 2012;8(1):43-46