Previous epidemiological studies of feline obesity have been restricted to small geographical areas of Great Britain. This study represents the first published description of the prevalence and risk factors for obesity from a nationally distributed population of cats. Data were gathered from 3227 cats through 47 primary companion animal veterinary practises. The overall prevalence of overweight/obesity was 11.5 per cent (95% confidence interval 10.4 per cent to 12.6 per cent) in cats attending the charity's clinics. Cats in Scotland appeared to have a greater age and neutered-adjusted prevalence compared with cats in England. Neutered status, being male and middle age (around 7 years), were all significant risk factors for feline overweight/obesity, although they did not fully explain an individual cat's risk of overweight/obesity. Breed was not found to be a statistically significant risk factor. Partial attributable fractions were calculated from each of the significant risk factors. Neutered status appeared to contribute the most to the prevalence of obesity, followed by prime/mature lifestage (3–10 years of age). Any interpretations of these findings should take into account the multitude of biases inherent in this study. Nevertheless, weight management following neutering appears to be very important to reduce the overall prevalence of overweight/obesity in this population of cats.