Background Elderly multiple organ dysfunction syndrome (MODS) patients receiving invasive mechanical ventilation have poor prognosis in intensive care units (ICUs).We studied the usefulness of four commonly used severity scores and extrapulmonary factors that affected weaning to predict outcome of such patients.Methods Clinical data of 197 patients on admission to ICUs (from January 2009 to June 2012) were used retrospectively.The Acute Physiology and Chronic Health Evaluation (APACHE) Ⅱ,APACHE Ⅲ,Sample Acute Physiological Score (SAPS) Ⅱ and MODS scores were calculated.All the patients were grouped into survivors and nonsurvivors according to the prognosis.Patients,who weaned from ventilator (n=154),were subdivided into a successful weaning group and a failed weaning group.The receiver operating characteristic (ROC) curves and Logistic regression was used for prognostic and weaning assessment.Results Based on the outcomes,the areas under the ROC of APACHE Ⅱ,APACHE Ⅲ,SAPS Ⅱ,and MODS were 0.837,0.833,0.824,and 0.837,respectively.The Logistic regression analysis revealed that the odds ratio (OR) of underlying lung diseases,serum albumin and creatinine,and the number of organ failures was 2.374,0.920,1.003,and 1.547.APACHE Ⅱ scores on admission performed excellent (ROC:0.921) on the weaning assessments.Conclusions APACHE Ⅱ and MODS systems were marginally better for evaluating the prognosis of elderly MODS patients who received invasive mechanical ventilation.Underlying lung diseases,serum albumin,serum creatinine and the number of organ failures were independent prognostic factors.Using the APACHE Ⅱ scores on admission before weaning may increase the likelihood of successful weaning.(ClinicalTrial.gov identifier NCT01802983).