REASONS FOR PERFORMING STUDY: To investigate upper respiratory tract function in horses, previously undergoing laryngoplasty (LP), using exercising video-endoscopy. OBJECTIVES: To evaluate arytenoid abduction and stability, diagnose any concurrent upper airway problems, and correlate these with the owners' perception of success. METHODS: Horses undergoing LP during a 6-year period at one hospital were initially included. Those available for re-examination were exercised for a duration and intensity considered maximal for their discipline using an over-ground endoscope. Resting and exercising laryngeal and pharyngeal videos were analysed blindly. Multivariable analysis was used to test associations between resting and exercising endoscopic variables, and also between endoscopic variables and owner questionnaire findings. RESULTS: Forty-one horses were included and 78% had a form of upper airway collapse at exercise, with 41% having complex forms, despite 93% of owners reporting the surgery to have been beneficial. Horses with poor abduction (grades 4 or 5/5) were 6 times more likely to make respiratory noise compared with those with good (grades 2 or 3/5) abduction (P = 0.020; 95% confidence interval [CI] 1.3-27.0), and those not having a ventriculectomy were 4.9 times more likely to produce respiratory noise post operatively (P = 0.048; 95% CI 1.0-23.9). Palatal dysfunction was observed in 24% of horses at rest, and 56% at exercise, with the diagnosis at rest and exercise significantly associated (P = 0.001). Increasing severity of pharyngeal lymphoid hyperplasia (prevalence 61%) was significantly associated with increasing arytenoid abduction (P = 0.01). Thirty-four per cent of horses had aryepiglottic fold collapse and 22% of horses had vocal fold collapse. CONCLUSIONS: Many horses that had previously had LP were diagnosed with upper airway abnormalities, despite the procedure being considered as beneficial by most owners. POTENTIAL RELEVANCE: When investigating cases of ongoing respiratory noise or poor performance following LP, exercising endoscopy must be considered. Continued respiratory noise may be associated with poor arytenoid abduction and not performing concurrent ventriculectomy.