Bariatric surgery is the most effective treatment for obesity. Its effects go beyond weight loss, in a high percentage of cases achieving remission of comorbidities associated with obesity and reducing mortality. However, not all patients achieve satisfactory weight loss or resolution of comorbidities and perioperative complications are a constant risk. Correct preoperative evaluation is essential to predict the likelihood of success and choose the most appropriate surgical technique for this purpose. The aim of this review was to ascertain which obese subjects will benefit from bariatric surgery taking into account body mass index, age, comorbidities, risk of complications and the impact of different bariatric surgery techniques.