Objective To determine prevalence of, and risk factors for, odontociastic resorptive lesions in cats seen in a private veterinary practice population. Design Population-based cross-sectional study. Animals 145 cats more than 1 year of age that underwent anesthesia for various procedures. Procedure Cats were evaluated under anesthesia for odontociastic resorptive lesions. Lesions were graded, using a published classification system. Clients completed a standardized survey on signalment, indoor-outdoor status, medications, diet during the past year, number of daily feedings, treat feeding, source of water, and oral hygiene practices. Results 48% of cats had resorptive lesions. Lesions were most commonly mandibular, and premolars were more often affected. Compared with cats without oral lesions, cats with oral lesions were more likely to be older, female, taking medications, drinking city (vs well) water, and playing less often with toys. In addition, cats without oral lesions were more likely to have owners who cleaned their teeth daily or twice a week and to be fed diets with higher magnesium, calcium, phosphorus, and potassium contents. Frequency of teeth cleaning was inversely related to the development of odontociastic resorptive lesions. Variables significantly associated with oral lesions were age and magnesium content of diet. Clinical Implications Older cats should be examined closely for odontociastic resorptive lesions. Clients should be advised on methods and frequency of teeth cleaning in cats to prevent lesions. Dietary nutrients may play a role in the development of odontociastic resorptive lesions in cats. (J Am Vet Med Assoc 1998; 212:392-395)