Background Inflammatory mechanisms had played an important role in the occurrence and prognosis of acute myocardial infarction, inflammatory mediators was associated with adverse outcomes of acute myocardial infarction. This study tested the hypothesis that in the acute phase of myocardial infarction with ST-segment elevation, neutrophil count and high-sensitivity C-reactive protein are predictive of angiographic morphologic features that indicate thrombus formation in the infarct-related artery. Methods This retrospective study included 182 consecutive patients with acute myocardial infarction and ST-segment elevation. Patients were assigned to a thrombus-formation group (n=77) and a non-thrombus-formation group (n=106). All patients had a Killip's classification <= 3 and onset < 12 hours prior to presentation. All the cases were going to undergo coronary angiography, including primary percutaneous coronary intervention, simple coronary angiography, or thrombolysis in a coronary artery (or arteries) or coronary artery bypass graft(s). Blood samples for measurement of high-sensitivity C-reactive protein and for routine blood laboratory studies were collected prior to coronary angiography. Results The levels of high-sensitivity C-reactive protein, total leukocyte counts, neutrophil counts, and neutrophil/lymphocyte ratios were substantially higher in the thrombus-formation group than in the non-thrombus-formation group patients (for each, P < 0.05). Stepwise Logistic regression analyses identified high-sensitivity C-reactive protein, neutrophil count, and neutrophil/lymphocyte ratio as independent predictors of thrombus formation in the infarct-related artery (for each, P < 0.05). Conclusions In patients with acute myocardial infarction, higher neutrophil counts, neutrophil/lymphocyte ratio, and levels of high-sensitivity C-reactive protein are predictors to indicate thrombus formation.