A patient specific guide block for a knee includes a plurality of bone interfacing portions and a cutting slot. The plurality of bone interfacing portions are configured to overlie portions of an end of a bone. The bone interfacing portions each have a surface that is generally a negative of the portion of the bone that the respective bone interfacing portion overlies. The bone interfacing portions are angularly offset from each other such that a first of the bone interfacing portions overlies an anterior portion of the bone, and a second of the bone interfacing portions overlies a portion of bone generally perpendicular to the anterior portion of bone. The cutting slot is oriented in a fixed position relative to the bone interfacing portions such that the cutting slot directs a cutting tool at a fixed angle and at a fixed depth relative to the bone interfacing portions.