Leukocytes play a pivotal role in the onset and progression of acute myocardial infarction (AMI). We evaluated the relationship between leukocyte count and coronary lesion severity of AMI. We carried out a retrospective study involving 815 patients with AMI undergoing primary percutaneous coronary intervention from 2005 to 2014 at a cardiovascular center. We recorded their risk factors, routine blood parameters, and cardiovascular events during hospitalization. When thrombus and nonthrombus burden groups were compared, leukocyte count (9.55 [7.80, 12.29] vs 10.70 [8.67, 13.04]×109/L, P = .005), neutrophil count (7.48 [5.65, 10.18] vs 8.61 [6.61, 10.80]×109/L, P = .001), and neutrophil–lymphocyte ratio (NLR; 4.99 [2.97, 7.16] vs 10.70 [8.67, 13.04], P = .003) were significantly different. Patients in the total occlusion group showed higher leukocyte count, neutrophil count, and NLR compared to the nontotal occlusion group. After multivariate logistic analysis, a neutrophil count ≥8.355 × 109/L was independently associated with high thrombus burden and total coronary occlusion. Leukocyte count, neutrophil count, or NLR was not significantly related to cardiovascular events during hospitalization. In conclusion, the neutrophil count might be an independent predictor of high thrombus burden and total coronary occlusion.