OBJECTIVE To develop a tenoscopic approach for desmotomy of the accessory ligament of the deep digital flexor tendon (AL-DDFT) in horses. METHODS Experimental. METHODS Cadaveric forelimbs (n=10) and 4 forelimbs from 2 horses anesthetized for terminal teaching procedures, and 12 forelimbs of 6 experimental horses. METHODS Saline distention of the carpal flexor sheath facilitated insertion of an arthroscope into the distal medial aspect of the sheath between the AL-DDFT and deep digital flexor tendon (DDFT). Location of an instrument portal on the lateral aspect of the metacarpus was identified with a needle. The lateral aspect of the AL-DDFT was transected and the arthroscope and instrument were switched to transect the remaining fibers on the medial aspect. Cadaveric specimens were dissected for evaluation. Experimental horses were monitored for 30 days postoperatively. RESULTS Minor complications including incomplete division of the AL-DDFT and shallow incision into the suspensory ligament were observed in some cadaver specimens. The AL-DDFT was completely transected in all experimental horses with no suspensory ligament damage. Mean±SD surgical time (incision to skin closure) was 28.3±11.8 minutes. On ultrasonographic examination, transection of the AL-DDFT was complete in all experimental horses. Minor DDFT fiber disruption was noted in 1 limb during ultrasound examination at day 30. CONCLUSIONS A tenoscopic approach through the carpal flexor sheath provided adequate access for desmotomy of the AL-DDFT.