The etiology of Osgood-Schlatter's disease remains a topic for debate. Previous studies by Ogden and Southwick (Osgood-Schlatter's disease and tibial tubercle development. Clin Orthop 116: 180 - 189, 1976) strongly support the concept of multiple microavulsions of the anterior surface of the developing ossification center of the tibial tubercle as the underlying cause. Orthopaedic literature fails to associate Osgood-Schlatter's disease with traumatic disruption of the extensor mechanism of the knee. Though the mechanism of injury for such trauma is as common as Osgood-Schlatter's disease itself, such occurrences are rare. Failure of the point of attachment of the patellar tendon in a patient with markedly symptomatic Osgood-Schlatter's disease tends to confirm the etiologic concept of Ogden and Southwick. Patients with markedly symptomatic Osgood-Schlatter's disease who engage in activities involving rapid deceleration or vigorous vertical acceleration are in a relatively high risk category for disruption of the extensor mechanism. Traumatic avulsion of the patellar tendon in such a patient establishes this relationship.