Subchondral bone density (by means of CT osteoabsorptiometry), and cartilage thickness (directly measured on photocopies of frozen sections), were examined in 30 human patellae, with an age range from 47 to 90 y. A surface demonstration of the distribution was prepared, and representative pictures produced by summation with a computer. Subchondral bone-density maxima were found in the proximal part of the lateral facet, and the density pattern interpreted as the expression of the long-term distribution of stress in the joint. It is reasonable to assume that cartilage thickness, of which two-thirds of the maximum values occupy a lateral position, is also dependent on the local stress. The 2 distributions show correlation coefficients > 0.5 in approximately a third of the cases we examined. Displacement of the higher values of cartilage thickness relative to the subchondral density maxima is attributed to incongruence in the medial part of the joint.