The present study aimed to examine associations of the testosterone/estradiol ratio, human leukocyte telomerase reverse transcriptase (hTERT) expression and telomerase activity of peripheral blood mononuclear cells (PBMCs) with aging and the presence of coronary artery disease (CAD). Telomeres in leukocytes are shorter in individuals with CAD than in healthy individuals of the same age. Levels of sex hormones are related to aging, and the ratio of testosterone to estradiol has been linked to CAD in men. Here we compared younger men (22 ± 2 yr, n = 26), middle-aged men (31 ± 5 yr, n = 35), older men without CAD (60 ± 10 yr, n = 30) and older men with CAD (63 ± 8 yr, n = 30) in terms of testosterone/estradiol ratio, leukocyte telomerase reverse transcriptase (hTERT) expression, activity of telomerase in peripheral blood mononuclear cells (PBMCs), and length of PBMC telomeres. Levels of hTERT mRNA of leukocyte and PBMC telomerase activity were significantly lower in older men than in younger or middle-aged men (p < 0.05). These two parameters, as well as testosterone/estradiol ratio, were significantly lower in older men with CAD than in all the other groups (p < 0.05). The sex hormone ratio correlated significantly with age, hTERT mRNA levels, PBMC telomerase activity and telomere length (p < 0.05). These results support the hypothesis that sex hormone balance is a biomarker of telomerase function, and that both of these parameters change as men age or develop CAD.