Objectives: Findings from several experimental studies in animals have suggested a protective action of testosterone on kidney function, but hard evidence for such an association in humans is scarce. We examined the association between testosterone levels and kidney function among adult men living in super-aged communities. Design, setting, participants, and measurements: We conducted cross-sectional study involving residents aged 40-80 years who participated in annual health check-ups in 2 communities. A total of 1031 men were recruited in 2010. Main exposure was salivary testosterone (sT) levels measured using an enzyme-linked immunosorbent assay. Main outcome was estimated glomerular filtration rate (eGFR) determined by age, gender, and serum creatinine levels. Results: For the 848 participants analyzed, median age and eGFR were 69 years and 69.1 mL/min/1.73 m(2), respectively. On comparison of 90th-percentile sT levels with lower levels, our general linear model with restricted cubic splines showed that lower sT levels were associated with decreased eGFR after adjustment for sociodemographic characteristics, comorbidities, and blood pressure. For example, fifth percentile sT was associated with decreased eGFR, with a difference in eGFR [-3.43 mL/min/1.73 m(2) (95% confidence interval, CI -6.02 to -0.84)] comparable in magnitude to the reduction in eGFR observed for a 6-year increase in age in our population. The association between low testosterone levels and decreased eGFR remained similar even when analyses were restricted to participants aged over 60 years (734 participants, median age 71 years). Conclusions: Results from our study indicated that having low testosterone levels was independently associated with reduced eGFR in adult men. Our finding of this association between low testosterone levels and reduced kidney function needs to be corroborated among persons with chronic kidney disease or in a longitudinal study. (C) 2016 AMDA - The Society for Post-Acute and Long-Term Care Medicine.