Cutting guide for a bone saw used to assure accurate bone cuts in implantation of prostheses and osteotomies. A cutting guide has a main body having guide elements that include a pair of guide surfaces that engage opposite sides of a saw blade. The guide surfaces guide the blade in a predetermined plane during the cutting process. In each pair of guide surfaces, the surfaces are spaced from one another along the plane a sufficient distance to enable the saw blade to pivot out of said plane away from engagement with at least one of the guide surfaces through an angle of at least 15.degree.. The cutting guide also includes means for attaching the guide to a bone surface to orient the guide elements with respect to the bone.