OBJECTIVES: To determine the influence of anxiety on the progression of disability and examine possible mediators of the relationship. DESIGN: Community-based observational study. SETTING: Women's Health and Aging Study I, a prospective observational study with assessments every 6 months for 3 years. PARTICIPANTS: One thousand two functionally limited women aged 65 and older. MEASUREMENTS: Anxiety symptoms were assessed using four questions from the Hopkins Symptom Checklist (nervous or shaky, avoidance of certain things, tense or keyed up, fearful). Participants who reported experiencing two or more of these symptoms at baseline were considered anxious. Anxiety as a predictor of the onset of four types of disability was examined using Cox proportional hazards models. Three models were tested: an unadjusted model, a model adjusted for confounding variables (age, race, vision, number of diseases, physical performance, depressive symptoms), and a mediational model (benzodiazepine and psychotropic medication use, physical activity, emotional support). RESULTS: Nineteen percent of women reported two or more symptoms of anxiety at baseline. Unadjusted models indicate that anxiety was associated with a greater risk of worsening disability: activity of daily living (ADL) disability (relative risk (RR) = 1.40, 95% confidence interval (CI) = 1.10-1.79), mobility disability (RR =1.41, 95% CI = 1.06-1.86), lifting disability (RR = 1.54, 95% CI = 1.20-1.97), and light housework disability (RR = 1.77, 95% CI = 1.32-2.37). After adjusting for confounding variables, anxiety continued to predict the development of two types of disability: ADL disability (RR = 1.41, 95% CI = 1.08-1.84) and light housework disability (RR = 1.56, 95% CI = 1.14-2.14). Finally, benzodiazepine and psychotropic medication use, physical activity, and emotional support were not significant mediators of the effect of anxiety on the development of a disability. CONCLUSION: Anxiety is a significant risk factor for the progression of disability in older women. Studies are needed to determine whether treatment of anxiety delays or prevents disability.