Of 118 patients with 151 knees treated for Osgood-Schlatter disease, fourteen patients (fifteen knees) had a distinct and separate ossicle at the proximal aspect of the tibial tubercle. This ossicle appeared after the child was first seen in all but three of the fifteen knees. When the ossicle failed to unite with the tubercle, the non-union was associated with local discomfort during activity and when direct pressure was applied on the tubercle. The symptoms did not respond to conservative treatment for an average of 3.8 years. Resection of the ossicle along with the adjacent bursa was followed by prompt relief of symptoms. Histological studies showed no evidence of avascularity. All ossicles were attached to the distal part of the undersurface of the ligamentum patellae and were separated from the tubercle by a bursa or scar tissue. The findings strongly support the concept that avulsion of the proximal cartilaginous part of the tibial tubercle is the cause of Osgood-Schlatter disease and they also suggest that once a separate ossicle is formed and becomes symptomatic, surgical excision is necessary to relieve the symptoms.