A randomly selected group of cat-owning households (n = 458) were interviewed to determine the diet of their cats (n = 644) in the week prior to the survey and to identify dietary and other factors which were associated with obesity. All cats were categorised by their owners as underweight, correct-weight or overweight and the weight of 127 cats was also recorded. Nearly all cats were fed commercially prepared dry pet food (90.5%) or canned pet food (84.6%) in the week prior to the survey. Nineteen percent of cats were classified as overweight. Although the make-up of a cat's diet was found not to be associated with its weight or weight category, cats fed dietary supplements or those which had not received a specific kitten diet when <6 months of age were more likely to be overweight after univariable analysis. Logistic multiple regression was used to investigate the effect of putative risk factors on obesity while controlling for other factors. Overweight cats were more likely to be cross-bred (OR = 2.1), neutered (OR = 2.8), living in houses with only one or two cats (OR = 1.8), male (OR = 1.4) and predominantly confined inside a house (OR = 1.4). Obesity is influenced by a variety of factors including host, dietary and management factors and these must be considered when developing weight control programmes for cats.