Observations made at the time of surgical exploration of the knee in five patients with osteochondrosis deformans tibiae have been described. In each child, a similar deformity was noted, namely, depression of the posteromedial aspect of the articular surface of the tibia. Whether this deformity is the result of pressure inhibition of enchondral ossification within the epiphysis itself, a secondary effect of growth retardation in the posteromedial growth plate, or a combination of both requires further investigation. The clinical findings of bowing, tibial torsion, sagging of the knee into varus, excessive prominence of the fibular head in the standing position, and a posteromedial rocking instability in slight fiexion are confirmatory clinical signs of intra-articular incongruity.