A 14-year-old boy presented with left anterior knee pain, which was aggravated by exercise and relieved by rest. On clinical examination, there was tenderness at the tibial tuberosity with reproducible pain on resisted active extension of the knee. Radiographs showed heterotopic ossification of the patellar tendon with irregularity and fragmentation of the tibial tubercle. Clinical and radiological findings were consistent with Osgood-Schlatter disease, which is a traction apophysitis of the tibial tubercle commonly occurring in adolescents. The clinical presentation and imaging features are discussed.