Background: The authors investigated the weight loss and maintenance in type 2 diabetic obese patients undergoing biliopancreatic diversion (BPD). Methods: Two series of diabetic and non-diabetic obese patients matched for gender, age and baseline body mass index (BMI) were evaluated prior to BPD, on the occasion of the regular follow-up visit at 1, 2 and 3 years following the operation, and at the fifth postoperative year. At each follow-up point, body weight (BW), BMI, and serum glucose concentration were measured. Results: In all type 2 diabetic patients, the serum glucose level fell to within the normal range at the first postoperative year and remained within normal limits without any medication throughout all the follow-up period. In preoperatively diabetic subjects, mean values of BW and BMI were closely similar to those of non-diabetic subjects at all follow-up points, and the stabilization weight was independently related to age and to initial BW values. Conclusions: In obese patients with type 2 diabetes, the glucose level steadily normalized in every case following BPD, and values remained unchanged throughout the follow-up period. After the operation, the type 2 diabetic obese patients experienced the same stable weight reduction as their non-diabetic counterparts.