Measurement gaps hamper understanding of late-life disability trends and dynamics. This article reports findings that validate the self-reported components of the disability protocol used in the new National Health and Aging Trends Study (NHATS). The protocol was designed to improve on existing measures by incorporating environmental aspects of disability, capturing a broader range of capacity to perform tasks and including participation restriction items. New items and summary measures demonstrate robustness over a short time period. Summary measures correlate as expected with age, sex, residential status, and performance-based constructs. Two factors, representing activity limitations and participation restrictions, were confirmed. The NHATS protocol preserves the ability to examine more traditional measures of functioning while offering new insights into how activities are performed.