AbstractBackground: Whether sex differences exist in the inflammatory response after ST-elevation myocardial infarction (STEMI) remains to be elucidated. We studied leukocyte profiles and their prognostic value in men and women presenting with STEMI. Methods: From a total of 552 consecutive STEMI patients, blood samples were collected at hospital admission. Linear regression was used to assess the relationship between leukocyte profiles and enzymatic infarct size. Cox regression was used to assess the association between leukocyte profiles and one-year mortality. Results: Women presented with higher lymphocyte counts (2.3·10⁹ cells/L (IQR 1.6–3.1) vs. 1.8·10⁹ cells/L (IQR 1.4–2.5), p = 3.00 ∙ 10⁻⁴) and percentages (21.1% (IQR 14.4–28.1) vs. 17.1% (IQR 12.3–24.3), p = 0.004). Lymphocyte to monocyte ratio (LMR) was also higher in women (3.25 (IQR 2.56–4.5) vs. 2.68 (IQR 2.08–3.59), p = 7.28 ∙ 10⁻⁷). Higher LMR was associated with lower peak CK-MB (β = −0.27 (95% CI: −0.50, −0.03), p = 0.026), lower peak troponin T (β = −0.45 (95% CI: −0.77, −0.13), p = 0.006) and lower one-year mortality risk (HR 0.35 (95% CI: 0.13, 0.96), p = 0.042). Conclusion: At admission for STEMI, women present with higher lymphocyte count and LMR. Higher LMR is associated with smaller infarct size and decreased one-year mortality risk and could be used as a biomarker to predict outcome.