Background: Peripheral dental caries is defined as macroscopic destruction of the calcified dental tissues and can cause considerable dental pathology and pain. It appears to occur at a high prevalence in Western Australian horses. At present, risk factors for the condition are poorly understood, making treatment and prevention difficult. Objectives: To assess the prevalence of and potential risk factors for peripheral caries in Western Australian horses. Study design: Cross-sectional, epidemiological study. Methods: A survey of 500 Western Australian horses was administered in two sections. The first section was completed by the owner and referred to the horse's signalment, diet and husbandry conditions. The second section was completed by veterinarians and focused on the horse's oral health. A multivariable logistic regression model was used to assess risk factors associated with peripheral caries. Results: Peripheral caries was present in 58.8% (95% confidence interval [CI] 54.5–63.1%) of surveyed horses. Breed was significantly associated with peripheral caries, with Warmbloods (odds ratio [OR] 0.44, 95% CI 0.24–0.82; P = 0.009) and Western breeds (OR 0.38, 95% CI 0.19–0.78; P = 0.008) being less likely to have peripheral caries than Thoroughbreds. Dietary risk factors included oaten hay (OR 2.90, 95% CI 1.87–4.53; P<0.001). A meadow hay-based diet was protective (OR 0.47, 95% CI 0.27–0.80; P = 0.005). Horses with access to quality pasture all year were less likely to have peripheral caries than horses without access to grazing (OR 0.31, 95% CI 0.15–0.66; P = 0.002), as were horses on groundwater compared with horses on rainwater (OR 3.35, 95% CI 1.65–6.78; P = 0.001), drinking water (OR 2.03, 95% CI 1.14–3.62; P = 0.016) or dam water (OR 3.53, 95% CI 1.08–11.53; P = 0.037). Peripheral caries was positively correlated with periodontal disease (OR 4.53, 95% CI 2.91–7.06; P<0.001) and feed packing (feed present between the teeth without significant periodontal pocketing) (OR 1.94, 95% CI 1.32–2.85; P = 0.001). Main limitations: Not every owner of eligible horses seen during the study period agreed to participate. An epidemiological study is unable to show causality. Conclusions: Western Australian horses have a high prevalence of peripheral caries. Management factors that may help to prevent or reduce peripheral caries include more access to quality pasture, use of groundwater, feeding on meadow hay and avoidance of oaten hay.