We tested the hypothesis that the use of a very-low-calorie diet (VLCD) in combination with behavior modification would promote long-term glycemic control in obese type 2 diabetic subjects. Thirty-six diabetic subjects were randomly assigned to a standard behavior therapy program or to a behavior therapy program that included an 8-week period of VLCD. The behavior therapy group consumed a balanced diet of 4200 to 6300 J/d throughout the 20-week program. The VLCD group consumed a balanced diet of 4200 to 6300 J for weeks 1 to 4, followed by a VLCD (1680 J/d of lean meat, fish, and fowl) for weeks 5 to 12. The VLCD group then gradually reintroduced other foods during weeks 13 to 16 and consumed a balanced diet of 4200 to 6300 J/d for weeks 17 to 20. Thirty-three of the 36 subjects completed the 20-week program and the 1-year follow-up. Use of the VLCD produced greater decreases in fasting glucose at the end of the 20-week program and at 1-year follow-up and greater long-term reductions in HbA1. The VLCD group also had greater weight losses at week 20, but weight losses from pretreatment to 1-year follow-up were similar in the two treatment groups. The improved glycemic control with the VLCD appeared to be due to increased insulin secretion, but further research is needed to confirm this.