We have conducted systematic studies to measure telomere length in human tissues of all types. Progressive telomere shortening with aging was studied in specimens of normal pancreas obtained at autopsy from 69 subjects aged 0 to 100 yr, and age-related shortening of telomere length at a rate of 36 base pairs (bp) per year was detected. Mean telomere length (+/-SD) was 13.9+/-1.4 kilobase pairs (kbp) in 16 neonates, as opposed to 8.4 kbp in 2 centenarians. Mean telomere length (+/-SD) in four age groups, 0-24, 25-49, 50-74, and 75-100 yr, was 13.5+/-1.5, 12.3+/-0.7, 11.3+/-2.5, and 10.7+/-1.8, respectively.