background: patients undergoing bariatric surgery may develop over time, some complications and anemia is an important one due to gastric resection, leading to iron, folic acid or vitamin b12 deficiency. aim: to determine the incidence of deficiency of vitamin b12 and other anthropometric and biochemical data comparing the preoperative and postoperative (six months) period in patients who underwent bariatric surgery with fobi-capella (roux-en-y) technique. methods: retrospective and descriptive analysis of 91 charts of patients who underwent surgery. it was collected personal information, date of surgery and pre-and postoperative (six months) values, weight loss, comorbidities, serum analysis of total cholesterol, triglycerides, glucose, vitamin b12, hemoglobin and hematocrit. for statistical analysis, it was considered significance level of 5% (p<0.05). results: it was found that there was a reduction in weight of 25,0% compared with the preoperative value and the average bmi was from 41,2±4,9 kg/m2 to 30,7±3,9 kg/m2. the most common co-morbidities were dyspnea (93,4%), spine alterations (61,5%), gastroesophageal reflux disease (57,1%) and sleep apnea (42,9%). biochemical tests for cholesterol, triglycerides and blood glucose, presented positive effect, changing from 240,2±36,1 to 162,5±19,1, 215,7±78,1 to 101,0±21,3 and 178,7±55,0 to 96,8±15,3 (mg/dl), respectively. for vitamin b12, hemoglobin and hematocrit, there was no statistical difference in relation to pre and post-operative time; however, was seen a reduction in vitamin b12 in 43 patients (47,2%). conclusion: the deficiency of vitamin b12 after six months of surgery could not be observed; this fact can be attributed to the use of nutritional supplements or to the short follow-up time after surgery.