obesity is a major public health problem and bariatric surgery is recognised as the most effective long-term treatment for significant weight loss and impact on associated co-morbidities, especially type 2 diabetes. However, the obesity epidemic does not save type 1 diabetes patients. Insulin resistance, usually characteristic of type 2 diabetes, can also be observed in type 1 obese diabetes patients. Bariatric surgery is therefore now being discussed in these patients, but the cases reported in the literature show inconsistent results on the impact of this surgery on type 1 diabetes. With the unique description of a patient who developed an autoimmune diabetes (LADA) a few years after a gastric by-pass was made, we wanted to explain the difficulties encountered in managing this type 1 diabetes: significant and rapid glycaemic changes due to changes in glucose absorption after such surgery and risks of hypoglycaemia. The introduction of an insulin pump coupled with continuous glycaemia measurement with automatic stopping of insulin infusion to limit hypoglycaemia has improved diabetes control. The literature review on the subject provides an understanding of the reasons for the discordant results described in type 1 diabetic patients with bariatric surgery. The various surgery, such as gastric by-pass, gastrectomy in sleeves and gastric ring, do not lead to similar changes in glucose absorption. After a gastric by-pass, a rapid and significant rise in blood glucose is observed when eating a test meal. The blood glucose rise is lower and later after a gastrectomy in sleeve. Finally, glucose absorption is not changed in patients with a gastric ring. Some studies postpone the evolution of patients who have undergone different types of bariatric surgery and thus confuse significantly different situations. Finally, to explain the inconsistent results found in the literature, it is also noted that the value of c-peptide and/or autoantibodies specific to type 1 diabetes are often not reported and the formal diagnosis of this diabetes can then be questioned. In conclusion, there are therefore no recommendations for the bariatric treatment of patients with type 1 diabetes and although the weight reduction is satisfactory, glycaemic control remains uncertain. In particular, it may not improve or even be made even more difficult, contrary to what is observed in type 2 diabetes patients after bariatric surgery and in whom diabetes can sometimes be redeployed. Careful documentation of the type of diabetes should be provided before such surgery and the implications of such surgery on the management of type 1 diabetes should be clearly exposed to patients.