1. Osteochondritis dissecans occurs primarily in males in the second decade of life, and is characterized by death of a special portion of the epiphyseal nucleus and articular cartilage of the knee and elbow joints. Other joints may be affected. The condition was bilateral in twenty per cent. of our cases. There is a great tendency to loose-body formation.

2. A clinical history of recurrent locking in a young man, without a history of trauma severe enough to cause a fractured cartilage, suggests osteochondritis dissecans. The diagnosis is rarely made on history and clinical examination alone; x-ray is diagnostic. The presence of loose bodies in a knee or elbow joint, whose source is not obvious, suggests a previous osteochondritis dissecans.

3. Our study of a small series of operated cases shows that radical operation gives a good result in eighty-eight per cent. of cases. Slumbering osteochondritis dissecans should be treated conservatively without operation, as spontaneous healing has been demonstrated in these cases. Long-standing cases with many free bodies and severe arthritis may not be cured by operation, because many of the subjective symptoms are due to the accompanying arthritis.