Alvin J. Detterline, MD; Jordan L. Goldstein, MD; John-Paul H. Rue, MD; Bernard R. Bach, Jr., MD J Knee Surg. 2008;21:106-115. ABSTRACT Osteochondritis dissecans (OCD) is a condition affecting the subchondral bone of joints with secondary effects on articular cartilage that results in pain, effusions, loose-body formation, and mechanical symptoms. Left untreated, OCD can lead to the development of degenerative arthritis secondary to joint incongruity and abnormal wear patterns. This article discusses the etiology of knee OCD lesions, clinical presentation, proper evaluation, and treatment options. Treatment of OCD may include nonoperative measures or operative procedures ranging from drilling or fixation of fragments to complex reconstruction procedures such as autologous chondrocyte implantation, osteochondral autograft, and fresh osteochondral allograft. Physicians must consider many factors, including the patients age and skeletal maturity, as well as size, location, and stability of OCD lesions to determine the proper course of treatment.