Diabetes mellitus is a complex disease with two dominant pathogenic lesions, one resulting from a failure of the beta cells of the islets of Langerhans and the other from resistance to the actions of insulin in peripheral tissue. Patients may demonstrate varying degrees of either or both lesions. Diet has an important place in the treatment of all diabetics. The most important objective is control of total caloric intake to attain and maintain ideal body weight. Obesity is diabetogenic. The diet of children with diabetes should allow them to grow and develop normally. Insulin-dependent diabetics must eat meals on a regular schedule. Carbohydrate intake should not be disproportionately restricted. Fat intake in diabetics and in nondiabetics should comprise only about 30% of total calories. Dietary instruction should not be a one-time affair. Physicians should seek the assistance of diet counselors when they are available. Many basic questions about diet and diabetes remain unanswered.