A retrospective analysis of patients who underwent knee arthroscopy was undertaken to determine the accuracy of clinical diagnosis when compared with arthroscopic findings, and to see whether any specific pathologies were difficult to diagnose. The preoperative diagnosis was compared with the operative findings and the accuracy, sensitivity and specificity of the clinical diagnosis calculated. Six hundred ninety-eight patients were included. The overall accuracy, sensitivity and specificity of clinical diagnosis was 99%, 70% and 99%, respectively. Ninety percent of patients underwent a beneficial procedure, while 10% had a normal knee diagnosed at operation. Medial meniscal tear was the hardest pathology to diagnose with accuracy, sensitivity and specificity rates of 82%, 92% and 79%, respectively. Clinical examination remains an accurate method of assessing whether patients would benefit from an arthroscopy, although the correct diagnosis may not be determined preoperatively, particularly if pain was located in the medial tibio-femoral joint.