Purpose: To review the current literature examining the relative merits of arthroscopy and MR imaging of the knee.Material and Methods: Allgapers comparing MR imaging with arthroscopy published within the last 10 years according to Medline were collected and read.Results: Technology has improved considerably during recent years allowing detailed non-invasive visualization of the knee. In particular, the development of cheaper whole-body and dedicated low-field MR units has opened up for non-invasive inspection of the knee at reasonable cost. Meniscal tears can be detected with accuracy rates of around 90% and rupture of the anterior cruciate ligament with accuracy rates of around 93% compared to arthroscopy. However, arthroscopy is not the ideal gold standard, since it has weak points, e.g. peripheral meniscal tears or osteochondritis without apparent damage to the cartilage.Conclusion: Based on the overwhelming literature it seems safe to conclude that MR examinations of the knee should be performed before arthroscopy is undertaken.The knee joint is a common site for morbidity as a result of trauma or degenerative disease with resultant temporary or permanent disability characterized by pain, immobility or reduction in previous sporting activity. Symptomatology, clinical examination and conventional film studies are often insufficient for an accurate diagnosis (12,40). Supplementary diagnostic procedures are often required to determine prognosis and allow appropriate management including conservative therapy.During the 1970s and the 1980s arthroscopy of the knee joint became the gold standard in diagnosing knee disorders. The advent of MR imaging has, in most institutions, led to the virtual abandonment of arthrography as a diagnostic procedure in the knee. Over the last 10 years MR has gained worldwide acceptance as the imaging method of choice for the non-invasive evaluation of the knee (21). It provides excellent anatomical detail (Fig. 1) unobtainable by any other imaging modality (Fig. 2).A vast number of papers have been published that examine the diagnostic accuracy of MR examinations of the knee but the exact role of MR remains unclear. In some institutions, diagnostic arthroscopy is not performed in the presence of a normal MR examination (22). This role for MR has been disputed (30, 37, 39) by some orthopaedic surgeons who favour arthroscopy. The purpose of this article is to review the current literature to examine the relative merits of arthroscopy and MR of the knee.The central question in this debate is the diagnostic accuracy of the 2 procedures but other issues such as time, patient comfort, risk and cost need to be taken into account. Arthroscopy is an invasive procedure requiring anaesthesia, carrying a small risk of infection and produces variable pain and reduction in movement in the days following the procedure. MR is non-invasive without known risk to the patient. It can be uncomfortable for the patient owing to prolonged examination time or claustrophobia but such problems are r...