Objective To compare the characteristics and risk factors of prognosis between elder and young patients with acute respiratory distress syndrome(ARDS)in intensive care unit(ICU). Methods The data of 150 patients meeting ARDS Berlin guideline who admitted to ICU of Affiliated First Hospital of Dalian Medical University from August 2011 to November 2013 were retrospectively analyzed. The patients over 65 years old were served as elderly group(n=78),and those younger than 65 years old were served as young group(n=72),and the patients were subdivided into survivors and non-survivors groups. The characteristics of patients at admission was recorded to investigate the characteristics of elder and young patients by univariate analysis. The univariate analysis was also conducted between different prognosis groups,and the risk factors of mortality were demonstrated by multivariate logistic analysis. Results Compared with the young group,the hospital length of stays〔days:27.0 (16.0,36.0)vs. 15.0(8.0,21.0),P=0.000〕,ICU length of days〔days:25.0(15.0,32.0)vs. 13.0(7.0,19.00), P=0.000〕,mechanical ventilation days〔days:19.0(11.0,27.0)vs. 8.0(5.0,15.0),P=0.000〕,the proportion of tracheotomy:〔39.74%(31/78)vs. 18.06%(13/17),P=0.003〕,the number of organ dysfunction(3.78±0.49 vs. 1.97±1.03,P=0.043)and creatinine(μmol/L:153.85±16.89 vs. 108.26±9.14,P=0.017)of elderly group were significantly increased. The mortality〔67.95%(53/78)vs. 59.72%(43/72),P=0.190〕and acute physiology and chronic health evaluationⅡ(APACHEⅡ)score(17.94±6.04 vs. 15.99±6.93,P=0.068)in the elderly group were higher than those in the young group but without the significant differences. The causes of death in elderly patients were mainly with respiratory failure;the mainly causes in young and middle-aged patients were complex with multiple organ dysfunction syndrome,circulatory failure and other reasons. APACHEⅡscore,the number of organ dysfunction,and maximum positive end-expiratory pressure(PEEP)in the non-survivors of the elderly group were significantly higher than those of the survivors〔APACHEⅡ score:19.45±6.00 vs. 14.72±4.83,the number of organ dysfunction:4.13±0.88 vs. 2.16±1.01,maximum PEEP(cmH2O,1 cmH2O=0.098 kPa):13.93±4.16 vs. 9.72±3.72, all P<0.01〕,and the proportion of tracheotomy and pH value were significantly lower than those of the survivors〔the proportion of tracheotomy:32.08%(17/53)vs. 56.00%(14/25),pH value:7.35±0.14 vs. 7.42±0.08,both P<0.05〕. Logistic analysis showed that APACHEⅡ score〔odds ratio(OR)=7.068,95% confidence interval (95%CI)=1.358-3.273,P=0.023〕,the number of organ dysfunction(OR=2.328,95%CI=1.193-4.520,P=0.029)were related with prognosis in elderly patients with ARDS. APACHEⅡscore,the number of organ dysfunction, blood lactate,maximum PEEP in non-survivors of the young group were significantly higher than those of the survivors〔APACHEⅡ score:18.12±6.88 vs. 12.83± 5.80,the number of organ dysfunction:3.16±1.23 vs. 2.55±1.29, blood lactate(mmol/L):4.84± 4.07 vs. 2.56±1.86,maximum PEEP(cmH2O):13.93±5.50 vs. 10.54±4.05, P<0.05 or P<0.01〕,and the pH value,hospital length of stays,ICU length of days were significantly lower than those of the survivors〔pH value:7.30±0.16 vs. 7.41±0.10,hospital length of stays(days):11.09±10.97 vs. 25.17±19.05,ICU length of days(days):8.0(5.0,13.0)vs. 20.0(12.0,31.0),all P<0.01〕. Multivariate logistic analysis showed that APACHEⅡ score was related with the prognosis in young patients with ARDS(OR=5.735, 95%CI=1.921-3.310,P=0.004). Conclusions Higher APACHEⅡscore and the number of organ dysfunction were independent predictors of worse outcome in elder ARDS patients. Higher APACHEⅡscore was the independent predictor of worse outcome in young ARDS patients.