The purpose of this study was to determine whether there is a difference in range of motion at the ankle and knee when measured in the clinic versus under anesthesia for ambulatory children with cerebral palsy. Dorsiflexion and popliteal angle were measured on 70 limbs in the clinic and under surgical anesthesia with the assessor blinded. For the group of patients under 11 years of age, dorsiflexion with the knee flexed significantly increased a mean of 9.5 degrees (P<0.05) and with the knee extended significantly increased 8.5 degrees when patients were under anesthesia compared with the clinical measures. Dorsiflexion angles did not change significantly between the two conditions for the group of patients older than 11 years of age. Mean popliteal angle did not change significantly between the two conditions for either age group.