A new comprehensive longitudinal study of aging, the National Institute for Longevity Sciences, Longitudinal Study of Aging (NILS-LSA) started in November 1997. The participants of this study will be 2, 400 residents aged 40 to 79 years who were ageand gender-stratified random samples selected from the NILS area. All participants provided written informed consent after a detailed explanation of the study. They will be examined at the NILS-LSA Examination Center every two years. Their first wave examinations will be finished by the end of March 2000. The examined variables number over 1, 000, including clinical evaluations, medical examinations, anthropometry, body composition, physical functions, physical activities, psychological assessments, nutritional analysis and molecular epidemiology. By the end of September 1999, 1, 643 men and women had completed their first wave examinations. J Epidemiol, 2000 ; 10 : S1-S9.