Introduction: The beneficial effects of weight loss and improved glycaemic control from bariatric surgery in the insulin-resistant, type 2 diabetic subject has been well documented. However, the effectiveness of bariatric surgery in obese patients with type 1diabetes is yet to be determined. Methods: We reviewed five obese female patients with type 1 diabetes mellitus who had undergone bariatric surgery. Laparoscopic procedures included gastric bypass (case 1), gastric banding (cases 2, 4 and 5) and sleeve gastrectomy (case 3). Results: Duration of diabetes was 2-28 years and duration of follow up after surgery was 4-119 months. Patients lost 14-26% of baseline body weight after surgery. Four of the 5 patients were able to reduce insulin doses (case 1: 130 to 57 U/day, case 2: 86 to 60 U/day, case 3: 46 U basal + 4 U:1 carbohydrate exchange to 25 U basal + 4-6 U with meals, case 4: data incomplete, case 5: 110 to 54 U/day). HbA1c improved in 3 patients (cases 1, 2 and 4) and deteriorated in the other 2 patients. Glycaemic response to bariatric surgery appeared unrelated to the type of surgery, duration of diabetes, baseline HbA1c and baseline BMI. Conclusion: Bariatric surgery in obese patients with type 1 diabetes mellitus does not appear to be universally associated with improved glycaemic control, despite weight loss. The predictors of glycaemic benefit from bariatric surgery in this group of patients require further investigation.