This study evaluated the extent to which rehabilitation outcomes and resource use can be predicted by functional status measures. Linear measures of motor and cognitive function were derived from the Functional Independence Measure for a sample of 27,699 patients undergoing initial rehabilitation. Admission functional status was consistently related to discharge function and length of stay, though the strength of these associations varied with impairment. Motor function was a stronger predictor of length of stay than was cognitive function for all impairments. However, the unique contribution of cognitive function was apparent for specific impairment groups. The predicted variance at discharge in motor function averaged 55%, 70% in cognitive function, and 20% in length of stay. These results support the use of functional status measures in the development of rehabilitation resource use models. Recommendations for future research are proposed.