We studied relationships between testosterone, metabolic syndrome, and mean carotid intima-media thickness (IMT) in aging men. We enrolled 935 men who had participated in a health examination. The median age was 57.0 years. Mean IMT showed a significant and negative linear correlation with testosterone (correlation co-efficiency = -0.067, p = 0.039). There was a significant increase in the percentage of men with hypogonadism in the second and third tertiles of mean IMT (p trend = 0.022). Logistic regression revealed a greater likelihood of hypogonadism in the third tertile mean IMT group when compared to the first tertile mean IMT group after adjusting for age and metabolic syndrome (OR = 1.700, p = 0.044). After adjusting for age and testosterone level, mean IMT was significantly higher in metabolic syndrome group as compared to non-metabolic syndrome group (0.733 mm versus 0.764 mm; p < 0.001). Mean testosterone level was significantly lower in metabolic syndrome group as compared to non-metabolic syndrome group after adjusting for age and mean IMT (5.52 ng/mL versus 4.89 ng/mL; p < 0.001). Mean IMT, testosterone, and metabolic syndrome were significantly and independently correlated with each other in aging male. Further studies are needed to confirm our results and to elucidate their causative relationship.