In this paper the authors discuss about prophylactic cholecystectomy in bariatric surgery. Having analyzed the mechanisms that increase bile lithogenicity after bariatric surgery, they evaluate advantages and disadvantages of prophylactic cholecystectomy. They present 53 obese patients submitted to biliopancreatic diversion and prophylactic cholecystectomy for surgical treatment of morbid obesity, because of the high incidence of pathological findings in the specimens and the absence of surgical complications related to cholecystectomy, the authors, in agreement with the literature, suggest routine cholecystectomy as an obvious adjunct to bariatric surgery. This attitude protects against the higher risk of subsequent cholecystectomy and against the misinterpretation of non-invasive diagnostic tests too, because of known limits of echography in obese people.