The disease I am about to describe is fairly common. I have seen approximately twenty or twenty-five cases in the past ten years. For an unknown reason the malady occurs almost exclusively in women. The history is quite characteristic and pathognomonic. These patients complain of pain in both knees only on ascending or descending stairs. Walking on the level is not painful in the least. On examination, movement of the knee joint in both extension and flexion causes no pain. The joint itself is not tender. On the other hand, a tender area is found on the inner tibia at the exact site of the insertion of the conjoined tendon of the sartorius, semitendinosus and gracilis tendons. Occasionally a slight swelling is found in this area but, as a rule, only tenderness is present. X-ray examination of the joint reveals no evidence of arthritis. In a few instances I made