Bariatric surgery (BS) is considered the only effective method to treat refractory obesity. This study evaluated the clinical-nutritional behavior of obese patients submitted to Roux-en-Y gastric bypass. This cross-sectional and analytical study evaluated weight, Body Mass Index (BMI), weight loss percentage (% WLP), excess weight loss (%EWL) and clinical manifestations. Results were evaluated considering a significance level of 5%. The sample was composed of 37 obese patients, mainly females (n = 26), median age of 40 years. Progressive and significant reduction of weight (128.2 +/- 21.5 vs. 104.4 +/- 18.2 kg), BMI (49.3 +/- 7.7 vs. 40.4 +/- 6.8 kg/m2) and consequent increase in the %WLP (18.6 +/- 3.9%) and %EWL (39.4 +/- 10.6%) were observed over 90 days of follow-up (P < 0.001). Significant increase in the number of patients presenting alopecia (10 vs. 18) and diminished events of dumping syndrome (9 vs 8) and xerostomia (21 vs. 11) were evidenced between 30 and 90 postoperative days. There was also significant reduction in the levels of fasting glucose (100.9 +/- 32.0 vs 83.0 +/- 12.3 mg/dL), total cholesterol (208.1 +/- 38.5 vs. 173.3 +/- 48.2 mg/dL), triglycerides (150.9 +/- 7.7 vs. 102.2 +/- 27.3 mg/dL), hemoglobin (13.3 +/- 1.4 vs. 12.6 +/- 1.0 g/dL) and hematocrit (41.1 +/- 3.8 vs. 39.2 +/- 3.3%) at 90 postoperative day compared to the preoperative period (P < 0.005). We conclude that BS is an effective treatment for weight loss and improved lipid and glycemic profiles. However, the frequency of alopecia and significant reduction in the hemoglobin and hematocrit levels at 90 posotperative day deserves attention.