With the notable increases at a global scale of the prevalence of obesity, a huge number of alternatives for its treatment have been developed. The surgical interventions have demonstrated to be effective in obtaining a signifi cant and sustained weight loss. Complications have been described after the surgical procedures, which include those derived directly from surgery, nutritional abnormalities like malnutrition and defi ciencies in micro and macro nutrients, metabolic abnormalities such as modifi cations in the calcium metabolism, formation of gallbladder stones and also some rare entities like nesidioblastosis; these adverse effects frequently affect the quality of life including vomit and Dumping syndrome, and the adaptive upheaval related to the need of modifying eating habits. Mortality is directly related to the surgeon’s expertise, and it has shown to be very low at places with important experience and an interdisciplinary group. In this publication we will review the adverse effects of the bariatric surgery, particularly the gastric bypass, and so their diagnosis and treatment, after a systematic search in www.pubmed.com of the articles published on the last seven years, in english, spanish or portuguese language and who where included in the following data bases: Hinary, Ovid and Cochrane. There were selected 28 papers which met the inclusion criteria. (Acta Med Colomb 2008; 33: 15-21).