Although controversial, seasonal variations in testosterone have been observed in several populations of men throughout the world. This finding might have an impact on screening and treatment of hypogonadism. We examined the circannual patterns of sex hormones in the Southwest United States. A prospectively assembled database of almost 11 000 patients in a men's health practice was used to collect data on testosterone, estradiol, sex hormone-binding globulin (SHBG), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and dehydroepiandrosterone-sulfate (DHEA-S). Patient age, address, and date of visit were recorded. Of note, testosterone-estrogen ratio (T/E ratio) and free testosterone were calculated values. The data were grouped by month and by season (3-month intervals beginning with June, July, and August as summer). Analysis of variance was used to compare hormone levels between seasonal and monthly data sets, with P < .05 regarded as statistical significance. Statistically significant differences in estradiol (P = .02), T/E ratio (P < .01), FSH (P = .02), and SHBG (P < .01) were observed between seasons. Peak-to-trough variations were as follows: 6% for estradiol, 16.5% for T/E ratio, 11.0% for FSH, and 11.6% for SHBG. The T/E ratio peaked in the spring and was at its nadir in the fall. No differences in testosterone (P = .21), LH (P = .25), free testosterone (P = .08), and DHEA-S (P = .11) were observed. Statistically significant evidence of variation in estradiol and T/E ratio were identified in the men included in this study. Although this is consistent with seasonal body habitus changes, physical activity levels, and hypothesized hormonal patterns, the variability reported in the literature makes further trials covering a broader geographic region important to confirm the findings.