The Functional Independence Measure for Children (WeeFIM) and the Pediatric Evaluation of Disability Inventory (PEDI) are the most commonly used measures of functional performance in children. The purpose of this study was to determine the concurrent validity of the instruments when used with children with developmental disabilities and acquired brain injury. The subjects were 41 children, age 1.3 to 9.5 years, who were receiving inpatient or outpatient services at a pediatric rehabilitation unit in Brisbane, Australia. Spearman correlation coefficients between the two tests were greater than 0.88 for self care, transportation/locomotion, and communication/social function. The high correlations indicate that the two tests measure similar constructs. Choosing between the tests depends on situational requirements and depth of information required.