The knee is the most frequent site of injury in volleyball players. More than 40% of high level players suffer overuse injuries during this activity; this particularly painful syndrome is caused by the amount of jumping typical in volleyball play, and in its training which aims at strengthening the quadriceps muscle. In volleyball players the extensor apparatus is subject to continuously high stress and the bone tendon junction, being the weakest point, is susceptible to lesion. The prevention and treatment of 'jumper's knee' requires a high degree of cooperation among trainers, doctors and athletes. Although volleyball is a sport without contact between players, traumatic acute injuries are more frequent and more serious than would be expected. It is therefore important to emphasise that volleyball must be considered among the high risk sports that expose the knee not only to twisting, but also to contact with other players. Generally, the lesions are caused by frequent jumps with loss of balance and a consequent 'one-footed' landing. There is no specific method of preventing knee instability. Accurate diagnoses, rest and rapid surgical treatment after the first injury are recommended in order to avoid chronic knee instability with subsequent meniscal lesions and post-traumatic osteoarthritis.