Based on a series of 48 patients with old untreated ruptures of one or both cruciate ligaments, the development of osteoarthrotic changes was demonstrated by radiography and at operation. The changes were similar to those seen in animal experiments and developed in the same sequence. Osteophytes occurred in knees with anterior cruciate insufficiency after about 2 years; significant osteoarthrotic changes occurred after longer periods, and particularly in knees with damage to both cruciate ligaments.