Background Biliopancreatic diversion with duodenal switch (DS) has been the standard surgical approach for the treatment of morbidly obese patients at our institution since the early 1990s. The published data, however, have shown the use of the DS to be limited to the treatment of super-morbidly obese patients (body mass index [BMI] ≥50 kg/m 2). The aim of the present study was to present our long-term results with the DS in patients with an initial BMI of <50 kg/m 2. Methods This was a retrospective study of all patients with a BMI <50 kg/m 2 who had undergone DS from June 1992 to May 2005. The data are reported as the mean ± standard deviation. Results The data from 810 consecutive patients, with a mean initial BMI of 44.2 ± 3.6 kg/m 2, were reviewed. The mean follow-up was 103 ± 49 months. Major perioperative complications occurred in 5.8% of patients, including 5 deaths (.6%). The initial excess weight loss was 76% ± 22%, and the excess weight loss was >50% in 89% of patients. Malnutrition required readmission in 4.3% and surgical revision in 1.5%. The prevalence of severe albumin deficiency (<30 g/L) was 1.1%, hemoglobin deficiency (<100 g/L), 1.6%, iron deficiency (<4 mmol/L) 2.1%, and calcium deficiency (<2 g/L) 3%. The percentage of patients “very satisfied” with the global result was 91%, and 37% would have preferred to lose more weight. Conclusion These results showed that in non super-obese patients, DS was very efficient in terms of weight loss and patient satisfaction. This was associated with a 1.5% risk of revision for malnutrition. However, nutritional deficiencies required frequent readjustment of supplements, particularly for calcium, vitamin A, and vitamin D.