Bariatric surgery is now recognized as a sure and effective way for weight reduction in morbid obesity. However some procedures induce intestinal malabsorption leading to enteric hyperoxaluria. So bariatric surgery could place these patients not only at risk for nephrolithiasis but also for oxalate induced nephropathy and chronic renal failure. Because of the growing incidence of obesity worldwide, physicians and patients should be aware of such potential complications. There is no mean to discuss this treatment because of its spectacular efficiency on obesity and its comorbidities. But it is necessary to choose the surgical technique according to the risk factors of the patients. Following surgery, preventive treatment strategies are indicated, such as modified dietary lifestyle and specific drugs as we suggested to limit or even avoid these complications. However observance could fail in the long term. In case of oxalate nephropathy, surgery may be proposed to restore the intestinal tract but with the risk of overweight relapse. To illustrate this matter, we report here significant observations of three patients, which, having successfully benefited from the same bariatric surgery, have presented lithiasic complications for two of them and oxalate nephropathy leading to chronic renal failure and hemodialysis for the third.