Previous research suggests that overweight patients with diabetes lose less weight than nondiabetics. We compared the response of obese women with NIDDM to nondiabetic controls, matched for age and weight, to a behavior weight loss program. Forty-three overweight women (20 NIDDM, 23 nondiabetic) participated in the study. NIDDM and nondiabetic subjects were treated together and received the same 16-week behavioral weight loss program. Dependent measures included weight, 3-day food records, physical activity, fasting plasma glucose, and questionnaires assessing eating behavior and depressive symptomatology. Weight loss of NIDDM and nondiabetic subjects at posttreatment was comparable (-7.4 +/- 5.3 kg vs. -6.4 +/- 3.8 kg, respectively). Changes in caloric intake, eating behavior, exercise and depressive symptomatology were also similar between the two groups. However, during the 1-year follow-up period, NIDDM subjects regained 5.4 +/- 6.1 kg compared to 1.0 +/- 6.7 kg for nondiabetics (p = .058). These data indicate that NIDDM subjects can lose as much weight as their nondiabetic peers during active treatment. Once treatment terminated, however, NIDDM subjects demonstrated poor weight loss maintenance. Thus the added motivation that comes from having diabetes and seeing improvements in glycemic control with weight loss were not sufficient to improve long term weight loss in diabetic subjects. A continuous care model of weight control may be particularly necessary for overweight patients with type II diabetes.