Osgood-Schlatter disease is a painful affection of the knee which touches particularly the active teenagers. Etiology of this frequent affection is unknown. This disease appears as an anterior knee pain and swelling started and worsened by the sports activities. Diagnosis is especially clinical. X-Rays, ultrasounds or IRM are not necessary for the diagnosis. Treatment is based on eviction of sports, analgesics and sometimes physiotherapy. Surgery is rarely proposed. Knee pain stops at the end of the growth. Long-term outcome is good for the majority of the patients. Some studies suggest a patella alta at the end of the growth, without an established correlation with knee arthritis.