Orthoses are the primary conservative treatment option for control of dynamic equinus in spastic cerebral palsy. Our purpose was to compare the effects of a fixed ankle-foot orthosis (AFO), a supramalleolar orthosis (SMO), and a no-brace condition, but including shoes. Gait analyses were performed on 11 children with spastic diplegia, using a system with four cameras and two concealed force plates. Ensemble averages of time-distance, kinematic, and kinetic parameters were obtained for each condition, and a repeated measures analysis of variance was performed (P < 0.05). Among the important findings were as follows: (1) AFOs significantly reduced ankle excursion, increased dorsiflexion angle at foot strike, increased plantar flexion moment in push-off, decreased ankle power absorbed during loading response, and decreased ankle power generated in push-off; (2) SMOs did not restrict ankle range of motion or significantly alter the power and moment values at the ankle joint. Although neither brace changed stride length and walking speed, AFOs did offer some biomechanical benefits to the child with spastic diplegia, whereas SMOs appeared to have very little measurable effect.