OBJECTIVE To explore the incidence,predictors,and prognosis of intra-aortic balloon pumping (IABP)-related thrombocytopenia in critically ill patients.METHODS This multi-center study used the eICU Collaborative Research Database V1.2,comprising data on ＞ 130,000 patients from multiple intensive care units (ICUs) in America between 2014 and 2015.A total of 710 patients undergoing IABP were included.Thrombocytopenia was defined as a drop in platelet count ＞ 50％ from baseline.From the cohort,167 patients who developed thrombocytopenia were matched 1∶1 with 167 patients who did not,after propensity score (PS) matching.The associations between IABP-related thrombocytopenia and clinical outcomes were examined by multivariable logistic regression.RESULTS Among 710 patients undergoing IABP,249 patients (35.07％) developed thrombocytopenia.The APACHE Wa score was a predictor of thrombocytopenia[adjusted odds ratio (OR) =1.09,95％ confidence interval (CO: 1.02-1.15].After 1∶1 PS matching,in-hospital mortality (adjusted OR =0.76,95％ CI: 0.37-1.56) and in-ICU mortality (adjusted OR =0.74,95％ CI: 0.34-1.63) were similar between the thrombocytopenia and non-thrombocytopenia groups.However,major bleeding occurred more frequently in the thrombocytopenia group (adjusted OR =2.54,95％ CI: 1.54-4.17).In-hospital length of stay (LOS) and inICU LOS were significantly longer in patients who developed thrombocytopenia than in those who did not (9.71 vs.7.36,P ＜ 0.001;5.13 vs.2.83,P＜ 0.001).CONCLUSIONS Among patients undergoing IABP in the ICUs,thrombocytopenia was not associated with a difference in inhospital mortality or in-ICU mortality;however,thrombocytopenia was significantly associated with a greater risk of major bleeding and increased in-ICU and in-hospital LOS.