Objective: Low testosterone levels in men have been associated with an increased risk of cardiovascular disease. We aimed to identify the association between serum testosterone level and premature coronary artery disease (CAD) and its predictors in young adult males. Methods: In this cross sectional study, consecutive, male candidates for coronary angiography with unstable angina, no previous CAD and age <= 45 years were included. Serum levels of free (FT) and total testosterone (TT) as well as demographic and cardiovascular characteristics were compared between the CAD-positive and normal coronary subjects. The cutoff,point for low IT was 2.5 ng/L. Additionally, the relationships between all the variables and the number of affected vessels and FT and TT and predictors of CAD were assessed. Results: In this study, 191 patients with premature CAD were compared with 94 normal coronary subjects. Patients in the CAD group were significantly older (41.59 +/- 3.79 versus 39.27 +/- 4.97 years; P-value < 0.01), and had higher rates of diabetes mellitus (P-value = 0.04) and dyslipidemia (P-value = 0.01). Serum levels of FT and TT were significantly lower in the CAD group than the normal coronary subjects (P-value < 0.01 for both). The rate of subjects with low TT increased by the number of the affected vessels (p-value for trend <0.01) and there was a significant correlation between the Gensini score and FT and TT (r = -0.37, P-value <0.01 and r = -0.34, P-value <0.01, respectively). After adjustment for confounders, the association between low TT and CAD remained significant (Odds ratio = 4.30, 95% confidence interval: 1.99-9.32; P-value <= 0.001) Conclusion: Low levels of testosterone were associated with premature CAD and its severity in young adults.