Background: The BioEnterics s Intragastric Balloon (BIB s ) System in association with restricted diet has been used for the shortterm treatment of morbid obesity. Aim of this study was to evaluate the real, short term, efficacy of the BIB for weight reduction in morbidly obese patients by using a prospective, double-blind, randomised, sham-controlled, crossover study. Methods: Patients were recruited from January 2003 to December 2003. After selection, they were randomly allocated into two groups: BIB followed by sham procedure after 3 months (Group A), and sham procedure followed by BIB after 3 months (Group B). All endoscopic procedures were performed under unconscious intravenous sedation. The BioEnterics Intragastric Balloon (Inamed Health; Santa Barbara, CA, USA) was filled by using saline (500 ml) and methylene blue (10 ml). Patients were discharged with omeprazole therapy and diet (1000 kcal). Patients were followed up weekly by a physician blinded to randomisation. In both groups mortality, complications, BMI, BMI reduction and %EWL were considered. Data were expressed as mean7s.d., except as otherwise indicated. Statistical analysis was performed by means of Student's t-test, Fisher's exact test or w 2 with Yates correction; Po0.05 was considered significant. Results: A total of 32 patients were selected and entered the study (8M/24F; mean age: 36.275.6 years, range 25-50 years; mean BMI 43.771.5 kg/m 2 , range 40-45 kg/m 2 ; mean %EW: 43.1713.1, range: 35-65). All patients completed the study. Mortality was absent. Complications related to endoscopy, balloon placement and removal were absent. Mean time of BIB positioning was 1572 min, range 10-20 min. After the first 3 months of the study, in Group A patients the mean BMI significantly (Po0.001) lowered from 43.571.1 to 38.072.6 kg/m 2 , while in Group B patients the decrease was not significant (from 43.671.8 to 43.172.8 kg/m 2 ). The mean %EWL was significantly higher in Group A than in Group B (34.074.8 vs 2.171%; Po0.001). After crossover, at the end of the following 3 months, the BMI lowered from 38.072.6 to 37.173.4 kg/m 2 and from 43.172.8 to 38.873.1 kg/m 2 in Groups A and B, respectively. Conclusions: The results of this study show that treatment of obese patients with BioEnterics Intragastric Balloon is a safe and effective procedure. In association with appropriate diet it is significantly effective in weight reduction when compared to sham procedure plus diet. The BIB s procedure can play a role in weight reduction in morbidly obese patients or in the preoperative treatment of bariatric patients.