The knee joint is the most complex joint in the human body and is also the joint that is most often injured. It is responsible for movement and for supporting the body during various routine as well as difficult activities. The anatomical structure of the knee that is most often injured is certainly the anterior cruciate ligament. This injury is rarely isolated and is often associated with an injury of the medial collateral ligament and an injury of the medial meniscus. A rupture of the anterior cruciate ligament can be complete or partial and symptoms of the injury include pain, swelling of the knee and difficult walking. The injury occurs due to hyperextension of the knee or in the case of a flexed knee when femur is moved backwards on the fixed tibia. Injury can occur during contact but also without contact. Non-contact injuries are more common. Assessment of an injury of the anterior cruciate ligament includes history and physical examination, which is additionally completed with tests. The three most commonly used tests for assessment and examination are Lachman test, pivot shift test and front drawer test. In addition, X-ray and magnetic resonance imaging are used during the actual diagnosis of the injury. Treatment of injury of the anterior cruciate ligament can be operative or conservative. The choice of treatment is not the same for every person. Factors to consider include age, severity of the injury, the person's activity level and associated injuries of the meniscus and other structures of the knee. Operative treatment is performed arthroscopically, the ruptured ligament is replaced with a tendon graft. Rehabilitation of the anterior cruciate ligament injury can be preoperative and postoperative. Postoperative rehabilitation can be divided into four phases. These are the early phase, the middle phase, the advanced phase and the phase of returning to activity. With rehabilitation, we must enable the patient to return to his activities that he had before the injury. The importance of the rehabilitation program is to protect and maintain ligament repair, and to maintain the patient's physical and psychological condition. Some of the therapeutic techniques used for this injury are hydrotherapy, cryotherapy, electrostimulation and magnetotherapy. Recovery varies depending on the individual, his intentions for later life and, of course, his physical condition or readiness. Rehabilitation lasts until the person fully recovers and returns to normal performance of activities. For active athletes, rehabilitation will take less time, while for recreational athletes, rehabilitation will be longer.