1. Thirteen new cases and fifteen from the literature illustrate the occurrence of an osteochondrosis similar to coxa plana and Madelung's deformity, but located at the medial side of the proximal tibial epiphysis.

2. The resulting abrupt angulation into varus with back-knee and internal rotation of the leg is usually confused with rickets.

3. The roentgenographic and pathological changes are like those of coxa plana and similar to those of chondrodysplasia, but quite different from those of rickets.

4. The changes may appear in the first year or two of life (infantile type) as a developmental exaggeration of the normal, with sloping epiphysis and beaklike recurving metaphysis.

5. A similar deformity may occur just before puberty (adolescent type), secondary probably to local trauma or possibly to infection.

6. The age at which the deformity is observed is more important than the causative factor in determining the roentgenographic appearance.

7. The roentgenographic findings of the infantile type gradually change to those of the adolescent, so that the two can be distinguished later only by the history.

8. Treatment should be directed toward the mechanical relief of strain until the deformity is stationary or until the epiphysis is closed.

9. A simple osteotomy is desirable in the correction of marked deformity. If it is done before the amount of angulation has become stationary, some degree of recurrence may be anticipated.