Abstract: An ankle-foot orthosis made of a carbon fiber reinforced material having low weight is carried on the front of the lower leg, extending over the lateral ankle and preventing plantar flexion. The orthosis may be worn under ordinary clothes and shoes and promotes a more natural gait pattern. The ankle-foot orthosis comprises a frame of thin flexible material extending over the front of the lower leg, anterior of the lateral ankle and beneath the sole of the foot and a supporting portion of rigid material extending over a narrow part of the front of the lower leg, anterior of the lateral ankle and beneath the part of the sole of the foot. The orthosis also comprises a fastening means for fastening the orthosis to the leg.