Patients who have diabetes mellitus have 2 times the incidence of an acute coronary syndrome (ACS) and 2 times the mortality rate after ACS compared with patients who do not have diabetes. Poor patient understanding of diabetes is believed to impede appropriate self-management, thus accelerating cardiovascular complications. We investigated the relation between patients' diabetes-related knowledge (DRK) and measurements of risk factor control and cardiac outcomes. Two hundred patients who had diabetes mellitus and ACS and were admitted to a university hospital were enrolled over a 9-month period. At enrollment, clinical and demographic data were recorded, and each patient completed a previously validated DRK assessment. Clinical outcomes data were obtained 6 months after enrollment. Years of education and DRK assessment score were moderately correlated (r = 0.496, p <0.0001). Glycosylated hemoglobin, low-density lipoprotein cholesterol, and body mass index showed no correlation with DRK assessment score (r = -0.045, -0.005, and 0.175, respectively), even after multivariable adjustment for differences in age, race, insulin requirement, duration of diabetes, and years of education. Rates of 6-month death (6.2% vs 9.7%) and death or myocardial infarction (15.5% vs 19.4%) were not significantly different between groups of patients stratified by DRK assessment scores (high vs low scoring groups). Thus, among patients who have diabetes and ACS, there is a moderate correlation between years of education and DRK. We found no correlation between DRK and measurements of risk factor control or 6-month clinical outcomes. New strategies must be developed to translate understanding of disease into better risk factor modification among patients who have diabetes and ACS.