Activities of daily living (ADL), a popular outcome assessment tool for studies of disabled populations, was evaluated for use in multicentered studies. The interobserver reliability of a modified Barthel Index of the ADL was evaluated on 18 stroke patients. Reliabilities between administrators of the ADL and between observers of the ADL administrations were r = .99 for total scores and r greater than .90 for most of the individual component items. The validity of ADL evaluation based on telephone interviews was demonstrated relative to ADL scores obtained on 72 patients in a direct test of their performance capabilities. The correlations between the performance-based ADL and the interview-based ADL were r greater than .97 for the total score and r greater than .85 for most of the individual items. The modified Barthel Index of the ADL is a reliable measure for assessing stable stroke patients, supporting its use in multicenter studies. In addition, the high validity observed in the telephone interview supports its use in longitudinal studies and large surveys where direct performance evaluation is not feasible or too costly.