Since most obese patients with type II diabetes are unable to achieve ideal body weight, this study examined whether more modest weight losses would provide a long-term benefit. Type II diabetic patients (N = 114) were treated in a behavioral weight control program and followed up for one year. Weight loss was significantly correlated with improvements in glycosylated hemoglobin values at posttreatment (r = .55) and one year (r = .51). Patients who lost more than 6.9 kg or had more than 5% reduction in body weight had significant improvements in glycosylated hemoglobin values at one year, while patients losing less weight had nonsignificant changes and those gaining weight had significant worsening. Thus, modest weight loss can have a long-term impact on glycemic control. However, the improvement in glycemic control for a given weight loss was greater initially than at one year, suggesting that energy restriction, in addition to weight loss, may contribute to initial improvement. Neither percent overweight nor diabetes treatment affected weight loss.