Background: Bariatric surgery is an effective treatment for several patients, but some may not achieve sufficient weight loss. We therefore evaluated predictors of adequate weight loss defined as ≥50% excess weight loss (EWL). Methods: Retrospective cohort study including patients who underwent sleeve gastrectomy (SG) or Roux-Y-gastric bypass (RYGB) followed for 12 months. Results: A total of 170 patients [81.2% female, age 42 years, 19.4% type 2 diabetes (T2D), body mass index (BMI) 49.4 kg/m2] were included. Type of surgery was SG (71.2%) or RYGB (28.8%). After surgery, the median BMI decreased to 34.9 (30.0-40.5) kg/m2. The median %EWL was 57.7 (41.6-69.7). Pre-operative weight loss was not associated with %EWL (P=0.25). Patients who achieved therapeutic success had a lower baseline median BMI of 48.0 (IQR, 42.9-51.6) kg/m2 whereas those who did not had a median BMI of 52.0 (IQR, 48.0-58.5) kg/m2 and the baseline BMI was correlated with the %EWL (P<0.001). Gender, age, and surgical method did not predict therapeutic success. The baseline BMI and T2D were the only predictors in logistic regression analysis. Conclusions: A lower baseline BMI and absence of T2D predicted therapeutic success and %EWL. RYGB and SG performed equally well, but the proportion of patients with T2D was higher in RYBG what may have influenced the outcome. Additional research is needed to evaluate the findings.