Purpose The purpose of this study was to evaluate glucose metabolism of normal human testis on $^{18}F$-FDG PET/CT and to assess possible correlations among age, the serum levels of sex hormones, and vasectomy. Methods $^{18}F$-FDG PET/CT was performed in 66 normal healthy men ($50.8{pm}13.6$ years, range 22-81), and mean standard uptake values (SUV) of $^{18}F$-FDG in testis and adductor muscle were measured. Testis-muscle SUV ratios (T/M ratios) were calculated. Serum levels of total testosterone, free testosterone, estradiol, and of sex-hormone binding globulin (SHBG) were measured. We searched for correlations between T/M ratios and age and the serum concentrations of sex hormones. $^{18}F$-FDG PET/CT was also performed in 32 vasectomized men ($55.7{pm}7.8$ years, range 38-71) and 52 nonvasectomized men ($55.4{pm}11.6$ years, range 37-72). Mean SUVs of testis and adductor muscle were measured, and T/M ratios were calculated. Results A significant age-related decline was found in T/M ratio (r=-0.509, p<0.0001). Serum levels of total testosterone and free testosterone were also found to be positively correlated with T/M ratio (r=0.427, p=0.0003; r=0.435, p=0.0003, respectively). The mean SUVand T/M ratio of vasectomized men were significantly lower than those of nonvasectomized men (p<0.0378 and p=0.0001, respectively). Conclusions Glucose metabolism in the testis in an adult population was found to be correlated with age, serum sex hormone level, and vasectomy history. These results indicate that testicular $^{18}F$-FDG uptake may have attributed to testicular function and testicular histology. Our findings may have important implications for the interpretation of testicular $^{18}F$-FDG uptake in the normal adult population.