Diabetes affects cats, especially older or overweight cats. As in humans, the incidence of diabetes in cats is increasing, and dietary components may play a role in its development. Trans-fatty acids (TFA), a particular type of fat, have been shown to contribute to diabetes and other health problems in humans. For this reason, starting in January of 2006, the amount of dietary TFA in human food products will be required on nutritional labeling in the United States. TFA are not naturally occurring, but are produced during processing of fats and oils for inclusion in foods, including pet foods. Currently little is known regarding the presence of TFA in animal diets. The objectives of this study are to determine the levels of TFA in 90 commercial diets commonly fed to cats, and to correlate the dietary TFA intake to serum indicators of diabetes in 60 cats. Results may lead to specific dietary recommendations regarding TFA levels in feline diets.