The knee joint is the largest joint in the human body and as such is subject to many injuries. One of the most common injuries in athletes and active people is jumper's knee or patellar tendinitis. it`s a part of overuse injuries. It is characterized by the pain that is often located on the top of the patella, but it can also be located on the tuberosity of the shin bone, it`s mostly initiated by the activity of muscle stretching, contraction of the quadriceps femoris muscle with resistance and during simple contraction. It occurs due to the accumulation of microtraumas over time, high-intensity training to which the tendons are not used, and degenerative changes. The occurrence of jumper's knee is influenced by both external and internal factors, such as the type of surface on which the athlete trains, the shoes he wears, muscle imbalance, flat feet and many others. The pain itself causes people to be unable to perform daily tasks and quit their sport activities, generally it causes reduced functionality. It can also occur when squatting, climbing or landing. The diagnosis is made by a careful clinical examination, most often by palpating the top of the patella and the tuberosity of the shin bone, but there are other methods, which are described in more detail in the upcoming text. Other diagnostic methods include ultrasound, radiographic examinations, magnetic resonance imaging and tremographic analysis. After the diagnosis, the rehabilitation process begins, which should be started as early as possible. It starts with a complete or partial sparing of the person from training, in accordance with the RICE method (Rest, Ice, Compression, Elevation). After that, focus is on increasing strength of the musculature of m. quadriceps femoris and flexibility of shortened muscles. The most popular exercise method is eccentric exercises with an incline because it simulates the healing process by putting additional stress on the patellar ligament. There are other treatment methods such as shock wave or electrotherapy. If none of the treatment methods succeeds, surgical treatment is unavoidable, mainly because pathological processes or tendon rupture have occurred. Nowadays, more and more attention is paid to the prevention of injuries. Firstly, it should start by eliminating internal and external factors, then the focus be on building strength and increasing the flexibility of muscles.