A customized human joint prosthesis replicating the primary contours and dimensions of a patient's bone is designed and manufactured utilizing an average anatomical bone shape. The average anatomical bone shape is generated by digitizing and storing in a computer memory the average three dimensional shape of a significant number of actual bone portions corresponding to the bone portion to be replaced by the prosthesis. Thereafter, the scale of the patient's bone is determined by measuring the outside dimensions of the patient's bone in at least one plane parallel to the longitudinal axis of that bone. The average anatomical shape then is adjusted to form a first synthesized shape which conforms to that scale. Subsequently, the actual shape of the bone of the patient is measured along a plurality of longitudinally spaced lines in at least one plane normal to the longitudinal axis of the patient's bone. The first synthesized shape is then adjusted to form a second synthesized shape conforming to the measured shape of the patient's bone. The second synthesized shape is manufactured by CAD/CAM or other suitable means.