High-carbohydrate, high-fiber (HCF) diets provide short-term benefits for selected individuals with diabetes. Long-term effects of HCF diets, however, have not previously been documented. The effectiveness and acceptability of HCF diets for 14 men with diabetes followed for 4 years as outpatients were assessed. Hospital HCF diets with 70% of energy as carbohydrate and 65 gm plant fiber daily lowered insulin doses, serum cholesterol, and triglycerides. Home HCF diets with 55% to 60% carbohydrate and 50 gm plant fiber daily sustained improvements throughout the observed period of up to 86 months. Of the 11 patients for whom diet adherence was evaluated, 9 had good to excellent adherence, 1 had fair adherence, and 1 had poor adherence.