Postmenopausal women consistently have higher phosphorus levels than similarly aged men. As it is known that estradiol induces phosphaturia in rodents, we evaluated the cross-sectional association of sex hormones with serum phosphorus in 1346 community-living older men (mean age 76) of which 18% had moderate (stage 3) kidney disease. Using linear regression with serum phosphorus levels as the dependent variable, we found that for each 10 pg/ml higher total estradiol level there was a statistically significant 0.05 mg/dl lower serum phosphorus when adjusted for age, ethnicity, testosterone, sex hormone-binding globulin, calcium, estimated glomerular filtration rate, intact parathyroid hormone, 25(OH) vitamin D, bone mineral density, and alkaline phosphatase. These results were similar in individuals with or without chronic kidney disease. Serum testosterone concentrations were also statistically significantly associated with lower serum phosphorus levels. We confirmed these results in an independent sample of 2555 older men, wherein these associations were not attenuated when adjusted for fibroblast growth factor-23 levels. Hence, our study of community-living older men suggests that estradiol may directly or indirectly induce phosphaturia in humans. The mechanism responsible for the association of testosterone with serum phosphorus remains to be determined.