There are few studies that investigate the usefulness of the preoperative intragastric balloon (IGB). This study will evaluate if pre-surgical weight loss with IGB reduces morbidity and mortality after surgery. Prospective randomised study of patients with morbid obesity treated with gastric bypass or vertical gastrectomy, with two arms: the balloon arm (B-arm), where an IGB was inserted within the 6 months before surgery, and the control arm (C-arm). The study included 66 patients: 65.6% women, 69.6% with bypass. Age: 43 years (SD 10.2) B-arm and 42.6 years (SD 9.2) in the C-arm. We found 34.4% therapeutic failures in IGB. The mean body weight loss, %EWL and BMI reduction before surgery was 16.2 kg (SD 9.84) B-arm versus 4.7 (SD 8.70) in the C-arm, 23.6% versus 4.7% (p