We studied 754 community-living persons, aged 70 years or older, who were nondisabled in 4 essential activities of daily living. Frailty, assessed every 18 months for 54 months, was defined on the basis of weight loss, exhaustion, low physical activity, muscle weakness, and slow walking speed. Participants were classified as frail if they met 3 or more of these criteria, as prefrail if they met 1 or 2 of the criteria, and as nonfrail if they met none of the criteria.