Data on the association of baseline thrombocytopenia (TP) with long-term outcomes of patients with acute ST-segment elevated myocardial infarction (STEMI) are still limited.Methods and Results:A total of 16,957 consecutive cases of patients with STEMI from multiple centers that participated in the China Acute Myocardial Infarction (CAMI) registry were included in this study. Two-year clinical outcomes were evaluated between patients with TP and those with a normal platelet count (PLT). Cases coexisting with baseline TP accounted for 2.1%. The rates of 2-year all-cause death (21.4% and 11.4%, P<0.001) and major adverse cardiovascular and cerebrovascular events (MACCE) (23.6% and 13.9%, P<0.001) were significantly higher in cases with TP, compared with the normal PLT group. After multivariate adjustment, compared with the control, cases with TP were not independently associated with 2-year all-cause death (HR: 1.21; 95% CI: 0.96-1.52; P=0.110) and MACCE (HR: 1.18; 95% CI: 0.95-1.47; P=0.132). After propensity score matching (PSM), the rates of 2-year all-cause death and MACCE were similar between the 2 groups (20.7% and 17.9%, P=0.317; 23.0% and 19.9%, P=0.288). Multivariable adjustment after PSM showed baseline TP was not independently associated with all-cause death (HR: 1.21; 95% CI: 0.88-1.67; P=0.240) and MACCE (HR: 1.21; 95% CI: 0.89-1.63; P=0.226). Patients with STEMI and baseline TP had higher rates of all-cause death and MACCE; however, baseline TP was not independently associated with 2-year adverse outcomes in patients with STEMI after multivariate adjustment and controlling for baseline differences.