BACKGROUND: Many older adults who are independent prior to hospitalization develop a new disability by hospital discharge. Early risk stratification for new-onset disability may improve care. Thus, this study's objective was to develop and validate a clinical index to determine, at admission, risk for new-onset disability among older, hospitalized adults at discharge. DESIGN: Data analyses derived from two prospective studies. SETTING: Two teaching hospitals in Ohio. PARTICIPANTS: Eight hundred eighty-five patients aged 70 years and older were discharged from a general medical service at a tertiary care hospital (mean age 78, 59% female) and 753 patients discharged from a separate community teaching hospital (mean age 79, 63% female). All participants reported being independent in five activities of daily living (ADLs: bathing, dressing, transferring, toileting, and eating) 2 weeks before admission. MEASUREMENTS: New-onset disability, defined as a new need for personal assistance in one or more ADLs at discharge in participants who were independent 2 weeks before hospital admission. RESULTS: Seven independent risk factors known on admission were identified and weighted using logistic regression: age (80-89, 1 point; ≥90, 2 points); dependence in three or more instrumental ADLs at baseline (2 points); impaired mobility at baseline (unable to run, 1 point; unable to climb stairs, 2 points); dependence in ADLs at admission (2-3 ADLs, 1 point; 4-5 ADLs, 3 points); acute stroke or metastatic cancer (2 points); severe cognitive impairment (1 point); and albumin less than 3.0 g/dL (2 points). New-onset disability occurred in 6%, 13%, 18%, 34%, 35%, 45%, 50%, and 87% of participants with 0, 1, 2, 3, 4, 5, 6, and 7 or more points, respectively, in the derivation cohort (area under the receiver operating characteristic curve (AUC)=0.784), and in 8%, 10%, 27%, 38%, 44%, 45%, 58%, and 83%, respectively, in the validation cohort (AUC=0.784). The risk score also predicted (P<.001) disability severity, nursing home placement, and long-term survival. CONCLUSION: This clinical index determines risk for new-onset disability in hospitalized older adults and may inform clinical care. © 2011, The American Geriatrics Society.