The atherosclerotic potential of the methyenetetrahydrofolate reductase (MTHFR) gene mutation 677 C --> T substitution remains controversial. In this study, we describe the association of this mutation in a Southern Texan patient population of multiracial ethnic background with risk and extent of coronary artery disease (CAD) as measured by luminal narrowing. Sixty nine patients who were 50 years or younger composed our population. Chi-square analysis was used to analyze the data and found a significant association between CAD and this mutation (P value=0.03). In addition, in the small number of patients in this study who had diabetes, those who had mutation have more severe disease than those without the mutation. This study highlights the potential cardiovascular prognostic significance of the MTHFR 677 C --> T in the studied population.