A review of lower-extremity length-discrepancy data in 803 patients demonstrated that not all discrepancies continue to increase at a constant rate with time. A classification of the developmental discrepancy patterns identified is presented: type I, upward slope; type II, upward slope-deceleration; type III, upward slope-plateau (type IIIA, downward slope-plateau; type IIIB, plateau); type IV, upward slope-plateau-upward slope; and type V, upward slope-plateau-downward slope. The patterns are dependent on the nature of the conditions causing the discrepancies and on the place and time of their occurrence. The distribution of the types of patterns in the various etiological groups is presented. The classification of developmental patterns illustrates the varying directional changes that can occur in these discrepancies and their dependence on underlying biological phenomena. Determination of the distribution of pattern types in the various conditions aids in planning the frequency of length-discrepancy studies. The patterns alone do not provide projections of final discrepancies, but when used in conjunction with the femoral-tibial length and growth-remaining charts of Green and Anderson they permit accurate projections of discrepancy to be made.