A 13-year-old Belgian jumping mare was presented with acute onset of severe left forelimb lameness after a jumping competition. Radiographic images showed the presence of periosteal new bone formation on the lateral radial eminence, while ultrasonographic images revealed a severe injury of the lateral collateral ligament of the elbow associated with severe proliferative synovitis of the humeroradial joint. The rehabilitation program consisted of hand walking for five weeks and progressive increase of controlled exercise duration for an additional 16 weeks. Therapeutic ultrasound and pulsed electromagnetic field were also applied. Repeated radiographic and ultrasonographic images after six weeks showed inactivity of the insertional pathology (smooth outline and homogenous radiopacity), marked improvement in the echogenicity and fibrillary pattern, reduction in size, resolution of the oedema, and joint distension. No signs of elbow osteoarthritis were detected. The horse retuned to its normal activity 22 weeks after the time of diagnosis. Injuries of the lateral collateral ligament of the elbow are rare and are frequently reported as traumatic and with poor prognosis. This case demonstrated that a severe lesion can result in a favorable prognosis for return to athletic activities with correct diagnosis and appropriate therapeutic multimodal approach.