Tendinitis of superficial digital flexor tendon (SDFT) represents a major cause of injury in the equine athlete. Although numerous treatments have been described, few are effective and a great potential remains for recurrence and, in certain cases, an abrupt end to the horse's athletic career. Recently, several experiments have focused on the therapeutic potential of mesenchymal stem cells (MSCs) in cases of tendon lesions. The aim of this study was to evaluate the possible clinical application of equine adipose tissue–derived MSCs (AD-MSCs) and autologous platelet-rich plasma (PRP) for the treatment of acute injuries of tendons in sport horses. Nine athlete horses with an injury of the SDFT were enrolled. Subcutaneous fat from each horse was collected, and AD-MSCs were isolated, characterized, and injected with autologous PRP in tendon injury. The evolution of tendinopathy healing was assessed by ultrasound. Horses underwent to a 6-month rehabilitation program. The ultrasound findings have shown indicative signs of a reparative process that led to the formation of tissue morphologically comparable with healthy tissue. Recurrences observed in only two of the nine horses treated occurred for reasons not related to treatment. In fact, in horse, the lesion occurred in the same tendon but at a different point from the first; another recurrence was caused by failure to comply with the rehabilitation protocol. Our study showed that therapy with AD-MSCs and PRP for treatment of tendon injuries in the athlete horse seems to be promising. However, the postoperative treatment of the patient is an essential support for the proper remodeling of the tendon.