The authors report a case of acute knee injury in a 14-year-old teenager. The X-ray showed a so-called Segond’s fracture: a small avulsed bone fragment, elliptical in shape, lying immediately below the external tibial plateau, a few millimeters from the lateral tibial cortex. The fracture site was in the portion of the tibial condyle which is linked to the middle third of the lateral capsule by meniscal tibial fibers. Clinical examination under anesthesia and subsequent arthroscopy revealed a total intrasubstance ACL (anterior cruciate ligament) tear close to the proximal insertion. The authors confirm Segond’s report of a possible association of this avulsion fracture with ACL injuries, even in adolescence.