Reasons for performing study: Horse misbehaviour is an important cause of poor performance in Pony Club horses, is associated with horse-related riderinjuries and has been implicated as a nonspecific presenting sign for musculoskeletal pain. Despite this, little is known about the incidence of and risk factorsfor misbehaviour in Pony Club horses.Objective: This study aimed to describe the incidence and types of misbehaviour in a cohort of Pony Club horses and to identify risk factors for misbehaviourduring riding.Methods: A prospective longitudinal study was conducted with 84 Pony Club horses from 41 families belonging to 7 Pony Clubs in one inland region ofAustralia. Owners recorded misbehaviour events and kept daily records of horse housing, exercise, nutrition, healthcare and disease status. Horses weresubjected to a monthly veterinary examination. Descriptive statistics were calculated to describe the incidence of misbehaviour, and multivariable logisticregression was used to assess putative risk factors.Results: Misbehaviour during riding occurred on 3% of days when horseswere ridden. On 52% of days with misbehaviour, the misbehaviourwas classified asdangerous.Risk of misbehaviour was independently increased on exercise days when the horse was competing, and in months when the horse was fat orobese, fed supplementary feed daily, grazed on paddocks with >50% of ground cover as green grass, exercised on 5 days per month or less, and ridden for atotal of 12 h or more in the month. No significant relationship was detected between misbehaviour and back pain.Conclusions: In populations such as the study population the risk of misbehaviour is higher in fatter horses, in horses with access to pastures with greatergreen grass cover, in those fed daily supplements, in horses receiving exercise less frequently, and during competition.Potential relevance: These results highlight the importance of considering horse body condition, nutrition and exercise in any investigation of horsemisbehaviour. In addition, recommendations based on these results could be used by veterinarians assisting horse owners to prevent misbehaviour. Fromthe perspective of recreational horse owners, behaviour is a key determinant of horse performance.