Introduction. Currently, bariatric surgery is the only effective therapy that leads to marked and sustained body weight loss. Although the morbidity rate after gastric bypass dropped, the postoperative complications are still a problem for the surgeons. Aim of the study. To appreciate the evolution of the first thirty days in patients submitted to the gastric bypass. Materials and methods. Observational retrospective study. Data of 388 patients with obesity associated or not with comorbidities submitted to the gastric bypass with 30 days follow-up starting from the date of the surgery. Results. The age average was 40,47±10,38 years. The mean preoperative body mass index was 43,83±8,19 kg/m2. The major complications were fistula (0,26%), gastrointestinal bleeding (3,35%), intra-abdominal bleeding (0,52%), acute gastric dilatation (1,29%), wound infection (2,83%) and deep vein thrombosis (1,55%). Conclusions. In the period of thirty days after surgery the overall complication rate was 9,8% and death occurred in 0%. Bleeding was the main complication and the leading cause of hospitalization in intensive care unit and reoperation.