We studied 1052 outpatients and inpatients receiving either Simethicone (n = 538) or placebo (n = 514) in University Medical Center of Ho Chi Minh city. Results: Bubbles are more diminishing in Simethicone group than placebo group (p < 0.00001). Conclusions: upper gastrointestinal endoscopic preparation with Simethicone is a safe and simple method which can improve upper gastrointestinal endoscopic visibility by diminishing the presence of bubbles