We assessed the interindividual diagnostic variance of 39 experienced arthroscopists by the Kappa Cohen interobserver variation analysis using videotapes of eight different patients with different diagnoses. Arthroscopically normal findings showed a relatively acceptable interobserver correlation. Pathological changes, in contrast, often showed very little correlation, especially in the synovial membrane of the suprapatellar recess, in the cartilage of the femoropatellar groove and the posterior cruciate ligament. In patellar alignment there was also great interobserver variation. CONCLUSIONS When comparing arthroscopic findings with other imaging techniques the above results should be taken into account. Furthermore, these results will affect the significance of medical expertise based only on pictures. In addition, medical cost billing, which is based on arthroscopic findings, has to take into account that a wrong diagnosis is possible and therefore charges will be wrong.