Background: There is significant evidence that reactive oxygen species play an important role in endothelial dysfunction, ischemia/reperfusion injury as well as in the pathogenesis of diabetes mellitus (DM). It is also known that vitamins C and E have substantial antioxidant properties. However, clinical evidence concerning this topic is insufficient so far. The aim of the present study was to determine if the administration of vitamins C and E influences the outcome in diabetic patients with acute myocardial infarction (AMI). Methods: Among 800 patients with AMI included in the MIVIT (Myocardial Infarction and Vitamins) study, 122 patients (15%) had confirmed DM. A retrospective analysis of the influence of vitamins C and E on 30-day cardiac mortality in patients with or without DM was performed. Results: There was a significant reduction in 30-day cardiac mortality in diabetic patients treated with antioxidant vitamins C and E [5 (8%) vs. 14 (22%); OR 0.32, 95% CI 0.11–0.93; p = 0.036]. Such an effect has not been observed in patients without DM [19 (6%) vs. 19 (6%); OR 0.97, 95% CI 0.51–1.85; p = 0.94]. Conclusion: The results suggest that early administration of antioxidant vitamins C and E in patients with AMI and concomitant DM reduces cardiac mortality.