Osteochondritis dissecans is a joint affection characterized by partial or complete detachment and necrosis of cartilage fragment and underlying bone from the articular surface. It is seen frequently in knee, elbow and ankle joints. Young males are most commonly affected. Also it develops not infrequently in children, but never in a child under 4 years of age. A case of osteochondritis dissecans which occurred in a 6-year-old boy is reported here. The patient had been sufferred from pain, swelling and progressive limitation of motion of the left knee. X-ray showed shadows like loose bodies on posteromedial aspect of the left knee. Clinically, possibility of tuberculous arthritis could not be rulled out. Loose bodies were removed, and almost detached ostechondral fragment was excised. At post-operative second week, crutch walking and physiotherapy were recommended.