The purpose of this study was to compare prospectively the distributions, validity, and discriminative ability of three pediatric outcome questionnaires. Consecutive patients completed the Activities Scales for Kids (ASK), the Child Health Questionnaire Parent Form (CHQ-PF-28), and the Pediatrics Outcomes Data Collection Instrument (PODCI). The scores of the three instruments were compared with each other and with parents' and clinicians' ratings. Of 210 patients, 166 (79%) completed the three questionnaires. The CHQ-PF-28 had a different distribution than the other two questionnaires and showed both floor and ceiling effects. The ASK and PODCI instruments were highly correlated and discriminated better than the CHQ-PF-28, with fewer floor and ceiling effects. Each questionnaire, however, seemed to be measuring slightly different things.