Of a series of 484 arthroscopies done with a special technique, we were able to inspect the posterior cruciate ligament satisfactorily in 96 per cent. The arthroscopic findings were checked at arthrotomy in 203 knees and the incidence of injury to the ligament in this group was 13.8 per cent. The over-all incidence of the injury in the series was 8 per cent. We made only one major diagnostic error: in this patient the ligament could not be fully visualized.