Telomere plays a critical role in protecting chromosomes. Building upon a unique large prospective cohort of healthy individuals undergoing health screening program in Taiwan, we propose this prospective longitudinal study to evaluate telomere length and the risk of cancer and diabetes. We propose three specific aims: 1) To determine the mean telomere length in peripheral blood leukocytes from 4,000 individuals at baseline, among whom we will include all those who have developed cancer (current incidence number 1,098) and will select 1,000 cases of type 2 diabetes (T20). We hypothesize that short telomere length at baseline is associated with increased cancer incidence and mortality, and increased risk of T20; 2) To measure the telomere length in an additional 2,000 samples at 5 years after their initial visit from the same 2,000 disease-free controls in Aim 1 and determine the association of demographic, epidemiological, clinical, and biochemical factors with the baseline telomere length and the rate of telomere erosion. We hypothesize that smoking, obesity, physical inactivity accelerate telomere attrition and lead to increased risk of cancer and diabetes.