Increasing evidence implicates inflammation as a risk factor for coronary artery disease. We determined whether an elevated leukocyte count is associated with an increased risk of death or reinfarction in stable patients with a past acute myocardial infarction (AMI). The current analysis is a substudy of the Multicenter Diltiazem Postinfarction Trial, which investigated the effect of diltiazem on mortality and reinfarction in 2,466 patients hospitalized for AMI. We included 1,294 patients in whom a leukocyte count was obtained 6 months after the index AMI. The composite end point of reinfarction or death was used as the primary end point of the study and reinfarction or cardiac death was used as a secondary end point. The study population was divided into 4 quartiles (Q1, Q2, Q3, and Q4) based on the leukocyte count. During a mean follow-up period of 25 months, 163 patients reached the primary end point: 8.7%, 10.9%, 14.0%, and 16.7%, in Q1, Q2, Q3, and, Q4 respectively (p = 0.01). After adjusting for potential covariates, Cox proportional-hazards analysis revealed that an increased leukocyte count was associated with an increased risk of both the primary end point (hazard ratio/1 quartile increase in leukocyte count, 1.26; p = 0.003; 95% confidence interval 1.08 to 1.47) and secondary end point (hazard ratio, 1.18/1-quartile increase; p = 0.05; 95% confidence interval 1.00 to 1.40). In conclusion, an increased leukocyte count measured in the stable post-AMI period is associated with an increased risk of cardiac events. These findings indicate that the leukocyte count may be another marker of an atherosclerotic inflammatory process that contributes to cardiac events in postinfarction patients.