Objective: To improve a self-administered questionnaire that includes 42 dichotomous items and measures activity limitations in rising and sitting down (R&S) in patients with lower-extremity disorders who live at home. Design: Cross-sectional study. Setting: Outpatient clinics of secondary and tertiary care centers. Participants: Patients (N=759; 47% men; mean age ± standard deviation, 60.7±15.2y) living at home, with lower-extremity disorders resulting from stroke, poliomyelitis, osteoarthritis, amputation, and complex regional pain syndrome type I. Interventions: Not applicable. Main Outcome Measures: (1) Unidimensionality, indicating that items assess only a single construct; (2) fit with the one-parameter logistic model (OPLM), yielding information about patient and item location parameters; (3) intratest reliability, indicating consistency of patients' item scores; and (4) content validity, indicating completeness with which the items cover the important aspects of the construct that they are attempting to represent. Results: Thirty-nine of 42 items: (1) loaded on 1 component (variance explained, 59%; item component loadings, ≥.51), (2) showed good fit with the OPLM (P=.15), (3) had a good intratest reliability (Cronbach α=.96), and (4) had a good content validity (all important aspects represented). Conclusions: A unidimensional scale that fits with the OPLM has been developed for measuring activity limitations in R&S in patients with lower-extremity disorders who live at home. © 2005 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.