OBJECTIVES: To define clinically relevant cutpoints for usual gait speed and to investigate their predictive value for health-related events in older persons. DESIGN: Prospective cohort study. SETTING: Health, Aging and Body Composition Study. PARTICIPANTS: Three thousand forty-seven well-functioning older persons (mean age 74.2). MEASUREMENTS: Usual gait speed on a 6-m course was assessed at baseline. Participants were randomly divided into two groups to identify (Sample A; n = 2,031) and then validate (Sample B; n = 1,016) usual gait-speed cutpoints. Rates of persistent lower extremity limitation events (mean follow-up 4.9 years) were calculated according to gait speed in Sample A. A cutpoint (defining high- (<1 m/s) and low risk (≥1 m/s) groups) was identified based on persistent lower extremity limitation events. The predictive value of the identified cutpoints for major health-related events (persistent severe lower extremity limitation, death, and hospitalization) was evaluated in Sample B using Cox regression analyses. RESULTS: A graded response was seen between risk groups and health-related outcomes. Participants in the high-risk group had a higher risk of persistent lower extremity limitation (rate ratio (RR) = 2.20, 95% confidence interval (CI) = 1.76-2.74), persistent severe lower extremity limitation (RR = 2.29, 95% CI = 1.63-3.20), death (RR = 1.64, 95% CI = 1.14-2.37), and hospitalization (RR = 1.48, 95% CI = 1.02-2.13) than those in the low-risk group. CONCLUSION: Usual gait speed of less than 1 m/s identifies persons at high risk of health-related outcomes in well-functioning older people. Provision of a clinically meaningful cutpoint for usual gait speed may facilitate its use in clinical and research settings. © 2005 by the American Geriatrics Society.