In most normal somatic cells, the terminal restriction fragments (TRF) length and age are inversely correlated, which can be used to determine individual age. However, very little is known about the quantitative relationship between human telomeres and age. The aim of the present study was to investigate age-, gender-, and ethnicity-related changes in telomere length in human peripheral blood leukocytes (PBLs). Changes with age in telomere lengths were assessed by Southern blotting. The results shown that telomeres shorten in human PBLs in an age-dependent manner (r = -0.913, P < 0.01). The formula for age estimation according to telomere shortening was Y = -16.539X + 236.287 (Y: age, year; X: mean TRF length, kb). We analyzed the mean TRF length in males and females and found that males had shorter telomeres than females. Moreover, we compared the TRF length of Tibetan and Han population in China and found that telomere length did not differ between 2 populations. We conclude that estimation of human age according to telomere shortening in PBLs is a novel method especially when there is no morphologic information, furthermore, the gender must be considered when age estimation is carried out based on telomere shortening.