There is increasing awareness of obesity and diabetes mellitus in cats that parallels the 'epidemic' of obesity and type 2 diabetes in humans. Likewise, understanding of the pathophysiology and management of feline obesity and diabetes has developed alongside and draws from human medicine. As in human medicine, overweight and obesity are associated with the development with diabetes; however, there are other genetic and environmental influences that contribute to this risk, some of which are shared. In cats, the body condition score appears to be a good diagnostic tool. It is reliable in the hands of owners and is likely to reflect visceral adiposity. However, the diagnostic label of feline obesity should be considered against the rate of success of any intervention, owner perspectives and impact on cat quality of life, as well as risk of future disease. The classification of human diabetes is evolving towards one that is more closely linked to disease outcome and therefore management. Consideration could be given to classifying the diabetes of hypersomatotropism and that associated with exogenous glucocorticoid administration in cats, separately in veterinary medicine. Rather regarding feline obesity and diabetes as models of human disease, a closer interdisciplinary 'One Health' approach between veterinary and human medicine is warranted to advance research and clinical care in this field.