OBJECTIVES: To estimate the prevalence and incidence of frailty and evaluate the effect of frailty on adverse outcomes in Chinese elderly adults. DESIGN: Secondary analysis of prospective cohort study. SETTING: Community in Beijing, China. PARTICIPANTS: Individuals aged 55 and older (N = 10,039). MEASUREMENTS: A Frailty Index (FI) was derived from 34 items using Rockwood's cumulative deficits method. A FI of 0.25 or greater indicated frailty. The clinical outcome was evaluated using a composite variable of any of the following adverse events: falls, hospitalization, activity of daily living disability, and death. RESULTS: The overall crude prevalence of frailty was 12.3% (95% confidence interval (CI) = 11.7-13.0%), and the standardized prevalence was 9.1% (95% CI = 8.6-9.7%). The crude incidence was 13.0% (95% CI = 12.2-13.9%), and the standardized incidence 10.8% (95% CI = 10.0-11.6%). Prevalence and incidence were significantly greater with age (P for trend<.001) and greater in women (P<.001) and urban residents (P<.001). Participants with lower education and having three or more diseases and taking four or more medications daily were more likely to develop frailty over follow-up (all P<.05). After adjusting for age, number of diseases, and smoking at baseline, the risk of any adverse event in 1 year in the frail group was 58% higher than in the nonfrail group (adjusted odds ratio = 1.58, 95% CI = 1.30-1.93, P<.001). CONCLUSION: A feasible FI that can be used in routine medical evaluation in a primary care setting was developed, and a 12.3% prevalence and a 13% incidence of frailty was demonstrated in community-dwelling Chinese older adults. Frailty is more common for urban and female residents in the oldest old group. Being frail significantly predicts geriatric adverse outcomes, indicating the importance of early screening and intervention in frail individuals in primary care.