Diabetes is a well-recognized and treatable risk factor for cardiac disease, and one of many comorbidities associated with obesity. The aim of this study was to evaluate the clinical outcome of a cohort of morbidly obese patients with documented diabetes who underwent laparoscopic Roux-en-Y gastric bypass. Fifty-nine patients with sufficient follow-up were included in the study. Mean preoperative duration of diabetes was 68 months. At 1 month postoperatively, mean excess body weight loss was 17 per cent with 29 patients (49%) showing improvement and 21 patients (36%) having remission of their disease. Mean excess body weight loss was 67 per cent at 12 months postoperatively with 25 patients (42%) showing improvement and 34 patients (58%) having remission of diabetes. Mean preoperative fasting blood glucose level decreased from 152 g/dL preoperatively to 100 g/dL at 12 months (P = 0.02), whereas glycosylated hemoglobin decreased from 7.9 per cent to 5.7 per cent, respectively (P < 0.01). Patients with remission of diabetes had a shorter length of condition compared with patients with only improvement (43 vs 103 months, P < 0.01). Weight loss associated with laparoscopic gastric bypass significantly improves diabetes control and results in discontinuation or marked reduction of antidiabetic medications in the majority of patients. Improvement in glucose control occurs as early as 1 month postoperatively.