Diabetes mellitus is one of the most common endocrine disorders in dogs and cats, with an estimated prevalence of 0.3-0.6%. Diabetes in many dogs has similarities to type 1 diabetes in humans and life-long insulin therapy is needed. The vast majority of cats suffer a type-2-like form of diabetes, which is characterised by insulin resistance and &bela;-cell dysfunction. Remission is possible in 25-50% of cats with adequate and early treatment. Relapse is possible at a later stage; however, remission may also last life-long. In some animals, diabetes develops as a sequela of another disease or problem such as pancreatitis, pancreatic carcinoma, hyperadrenocorticism, acromegaly (in cats), diestrus and steroid application. Diabetes is a disease of middle-aged to old animals; in cats the male gender is overrepresented. Some dog breeds and the Burmese cat have a higher risk of diabetes due to genetic predisposition. Diabetes is diagnosed by means of hyperglycaemia and increased fructosamine. Further work-up should include a search for any concurrent disease. The therapy consists of insulin BID, diet, weight loss, cessation of diabetogenic drugs and treatment of concurrent diseases. In most cases, adequate glycaemic control can be achieved within 2-3 months; remission usually also occurs during this time. Initially, frequent re-evaluations and adjustments of the insulin dose are required.