An osteotomy guide and surgical kit for performing a tibial osteotomy are provided, wherein the osteotomy guide comprises two or more rows of guide holes formed therethrough for attaching the guide onto a pair of guide pins in a predetermined relation to a tibia; a transverse slot, defining a transverse cutting plane; and a plurality of oblique slots angularly offset from the transverse slot, each oblique slot defining an oblique cutting plane. Additional features of the surgical kit include a transverse member adapted to pass through the transverse slot, which can be either a modified saw blade or a separate removable plate, and a locking device on the osteotomy guide for lockably engaging the transverse member and positioning the osteotomy guide at a predetermined location relative to the transverse member. A measurement guide hole is also provided in the same plane as the transverse slot so that accurate measurement of the tibial depth can be accomplished. At least two fixation holes are formed through the osteotomy guide in directions which are non-parallel to the guide holes so that additional fixation pins may be placed into the tibia for more stable positioning of the osteotomy guide. An alternative embodiment of the osteotomy guide is also provided which includes a removable clamp to lock the guide onto the guide pins prior to making the oblique cut. Methods of performing an osteotomy using the preferred and alternate embodiments of the osteotomy guide are also provided.