In ambulatory children with cerebral palsy (CP), practitioners often examine outcomes using measures related to functions necessary for daily life. The Gross Motor Function Measure (GMFM) Dimensions D and E, Pediatric Outcomes Data Collection Instrument (PODCI) Parent and Child versions, Gillette Functional Assessment Questionnaire (FAQ) Walking subscale, Functional Independence Measure for Children (WeeFIM), Pediatric Quality of Life Inventory (PedsQL), temporal-spatial gait parameters, and O2 cost during ambulation were selected for study. Cross-sectional data were collected in a prospective multicenter study of 562 participants with CP (339 males, 223 females), between 4 and 18 years of age (mean age 11y 1mo). There were 240 classified as Gross Motor Function Classification System Level I, 196 as Level II, and 126 as Level III. The tools that had the best interrelationships and underlying constructs predominately measured changes in physical function. These included portions of the FAQ, Parent PODCI, WeeFIM, and GMFM. GMFM Dimensions D and E exhibited a very strong relationship. Temporal-spatial gait parameters and O2 cost measures represented a different construct of physical function. The Child PODCI reports and both the Parent and Child PedsQL reports did not relate well to other measures, suggesting a pattern of answers not related to question content. The Parent PODCI, the FAQ Walking subscale, and GMFM Dimension E were found to be an appropriate minimum set of instruments for assessment of functional outcomes in patients with ambulatory CP.