The biodynamic total hip prosthesis which was devised in 1977-78 and implanted in 1979 was derived from a series of experimental studies and a lengthy clinical experience, both dating back to 1968. This prosthesis introduced two new and original concepts into the field of prosthetic hip surgery: 1) the biequatorial design of the cup; 2) the preservation of the femoral neck. This prosthetic system is based on maximum preservation of the bone stock as well as hip function. The biequatorial cup allows for positioning corresponding to that of the normal acetabulum. The femoral component incorporates features (collar, sagittal and frontal angulation, external surface, etc.) which facilitate proximal cortical fixation and cancellous metaphyseal biological anchoring, thus ensuring total adhesion. The average 3.5 years follow-up (maximum 7 years, minimum one year) in 280 cases confirms the effectiveness of this prosthesis and the validity of the basic principles on which it is founded.