OBJECTIVES To evaluate the relationship between intervening illnesses and injuries leading to hospitalization and restricted activity, respectively, and prolongation of disability in four essential activities of daily living in newly disabled older persons. DESIGN Prospective cohort study. SETTING Greater New Haven, Connecticut. PARTICIPANTS Community-living persons aged 70 and older who had at least one episode of disability from March 1998 to June 2013 (N=632). MEASUREMENTS Disability and exposure to intervening illesses and injuries leading to hospitalization and restricted activity, respectively, were assessed every month. Prolongation of disability was operationalized in two complementary ways: as a dichotomous outcome, based on the persistence of any disability, and as a count of the number of disabled activities. RESULTS During a median follow-up of 114 months, the 632 participants experienced 2,764 disability episodes. The mean exposure rates for hospitalization and restricted activity were 80.7 (95% confidence interval (CI)=73.7-88.4) and 173.6 (95% CI=162.5-185.5), respectively, per 1,000 person-months. After adjustment for multiple disability risk factors, the likelihood of disability prolongation was 2.5 times as great (odds ratio (OR) 2.54, 95% CI=2.05-3.15) for hospitalization and 1.2 times as great (1.21, 95% CI=1.06-1.40) for restricted activity as for no hospitalization or restricted activity, and the mean number of disabilities was 35% (risk ratio (RR)=1.35, 95% CI=1.30-1.39) greater in the setting of hospitalization and 7% (1.07, 95% CI=1.05-1.09) greater in the setting of restricted activity. CONCLUSION Intervening illnesses and injuries leading to hospitalization and restricted activity, respectively, are strongly associated with prolongation of disability in newly disabled older adults. Efforts to prevent and more-aggressively manage these intervening events have the potential to break the cycle of disability in older persons.