From 2006 arthroscopies of the knee, carried out between 1978 and 1983, 196 cases (9.8%) presented with traumatic haemarthroses and clinically stable capsular ligaments. A comparison was made between the standard clinical examination including routine X-ray and arthroscopy carried out under anaesthesia. Arthroscopy, as a diagnostic procedure, was found to be clearly superior with the same minimal complication rate. The standard clinical examination was inferior and inadequate particularly in cases with isolated torn anterior cruciate ligaments, in chondral injuries, and luxation of the patella. Thus, in a recent trauma with haemarthrosis and a clinically stable ligament apparatus, acute arthroscopy is the investigational method of choice, preferably carried out under anaesthesia.