Tongue-ties are frequently used in an attempt to prevent dorsal displacement of the soft palate (DDSP). The aim of this study was to determine the efficacy of a tongue-tie in horses clinically affected with the disorder. Videoendoscopic recordings and measurements of respiratory airflow were made simultaneously during high intensity treadmill exercise in 6 Thoroughbred racehorses with confirmed DDSP, with and without a tongue-tie. DDSP was confirmed in all 6 horses without the tongue-tie but occurred in only 4 horses with the tongue-tie in place. In one horse the palate displaced only on slowing down after intense exercise and in the other horse DDSP did not occur although palatal instability remained. The presence of the tongue-tie did not result in any significant alteration in run-time to fatigue or in any of the respiratory variables measured. The results suggest that the use of a tongue-tie may prevent DDSP in individual horses although it is not effective in the majority, consistent with the widely accepted anecdotal reports of success rates for its use. Where DDSP was not prevented, application of a tongue-tie did not improve ventilation.