Arthroscopy provides useful information in various knee problems in which the diagnosis and treatment are in doubt and these informations help in planning appropriate treatment for the patient. Arthroscopy and examination under anesthesia should always be considered to help in the diagnosis of acute injury of the knee. Arthroscopy provides a more accurate diagnosis than clinical examination alone and is especially valuable for assessing the patient with haemarthrosis of the knee. Although arthroscopy was initially considered a contraindication in acute knee disorders, it has been shown to be of great diagnostic value in the acute knee and its use in these conditions has been widely recognized. Arthroscopic lavage and debridement in patients of osteoarthritis produce significant improvement regarding pain, function and range of movement. In well selected patients arthroscopic debridement may be a valuable method for providing transient relief of symptoms and when appropriate it may lengthen the useful lifetime of a knee joint.