Although inflammation is involved in the pathogenesis of acute coronary syndromes, the extent of inflammation is not routinely assessed, and its prognostic implications in patients with non-ST-segment elevation acute coronary syndrome have not been investigated in depth. We analyzed the prognostic implications of an elevated white blood cell count (WBCc) in patients with moderate and high-risk non-ST-segment elevation acute coronary syndrome undergoing an early invasive strategy in the large-scale Acute Catheterization and Urgent Intervention Triage StrategY trial. The WBCc at admission was available for 13,678 of 13,819 patients (98.9%). The patients in the upper tertile of the WBCc had an increased risk of 30-day major bleeding, 1-year mortality, and definite/probable stent thrombosis compared to those in the mid or lower tertiles. On multivariate analysis, the WBCc was an independent predictor of 30-day major bleeding and 1-year cardiac, noncardiac, and all-cause mortality. The association between the WBCc and cardiac mortality was present in multiple prespecified subgroups, with no significant interaction between the WBCc and age, gender, diabetes, smoking, renal dysfunction, elevated baseline biomarkers, antithrombotic therapy, revascularization, and Thrombolysis In Myocardial Infarction risk score. The WBCc remained an independent predictor of mortality after adjusting for bleeding, C-reactive protein level, and angiographic variables, including left ventricular ejection fraction, Thrombolysis In Myocardial Infarction flow, and number of diseased vessels. The WBCc significantly improved the prognostic accuracy of the Thrombolysis In Myocardial Infarction risk score, with a net reclassification improvement of 11% (p <0.0001). In conclusion, in patients with moderate- and high-risk non-ST-segment elevation acute coronary syndrome, an elevated admission WBCc was an independent predictor of 30-day major bleeding, and 1-year cardiac, noncardiac, and all-cause mortality.