The Model Systems assessed the functional level of individuals with traumatic brain injury (TBI) using the Disability Rating Scale, the Functional Independence Measure, and the Functional Assessment Measure at admission and discharge from acute inpatient rehabilitation. In this article, the reliability, validity, and other characteristics of the three scales are reviewed. Data were available on six indices of severity of injury, ie, Glasgow Coma Score (rated within 24 hours of injury), days in coma, days in posttraumatic amnesia (PTA), Revised Trauma Score, computed tomography pathology, and the Levels of Cognitive Functioning Scale. (LCFS or “Rancho Scale” rated at rehabilitation admission). Strong correlations between the functional measures and length of coma, length of PTA and LCFS were demonstrated. Findings provided further evidence for the validity of the scales.