The purpose of this study was to investigate the use of the heart-rate (HR) version of the energy expenditure index (EEIHR) as a proxy for measurement of walking oxygen consumption (VO2) in children with cerebral palsy (CP). Thirteen children (eight males, five females; mean age 11 years 2 months [SD 3 years], age range 6 to 15 years) with hemiplegic CP, participated in this study. The study was conducted over three sessions. During session 1, participants were familiarized with testing procedures and given 5 minutes of treadmill walking practice. In session 2, participants completed three 5-minute walking bouts on the treadmill at 0.67m·s-1 to familiarize themselves with treadmill locomotion. During the final session participants walked at 0.67, 0.89, and 1.12m·s-1 for 5 minutes while gross oxygen consumption (gross VO2; walking VO2/speed), net VO2 ([walking VO2–resting VO2]/speed), and EEIHR ([walking HR–resting HR]/speed) were measured during the last 2 minutes of each bout. Correlational analyses indicated no relationship (p>0.05) between measures of gross VO2 and EEIHR at each speed. Although no association was evident between net VO2 and EEIHR at 0.67 and 0.89m·s-1, a moderate relationship (r=0.64; p<0.05) was present between these variables at 1.12m·s-1. Examination of individual data revealed that most participants displayed an unmatched pattern of response between net VO2 and EEIHR. Our results suggest that caution should be applied when using EEIHR to estimate walking energy expenditure in children with CP.