Objectives: Both obesity and laparoscopic surgical methods are predisposing factors for atelectasis. We aimed to evaluate with lung ultrasound (US), the incidence and location of atelectasis in patients undergoing laparoscopic bariatric surgery. Methods: Patients (n=143) between the ages of 18 and 65, BMI ≥30, and ASA 2-3 who underwent laparoscopic bariatric surgery were included in our prospective observational study. According to the lung US protocol, a total of 12 areas (anterior, lateral, and posterior areas divided into upper and lower regions) were scanned in both hemithorax preoperatively and in the 1st h after surgery. In the perioperative period, vital parameters and mechanical ventilation parameters were recorded. The images were evaluated blindly by two anesthesiologists experienced in lung US according to the modified lung US scoring system (LUS). Results: When the pre-operative and post-operative LUS scores were compared, we observed an increase in the LUS score in all areas except for both anterior upper areas (p<0.001). This increase was more pronounced, especially in the posterior and inferior parts of the lungs. We found the frequency of atelectasis to be 81.1%. The pCO2 values were increased (p<0.001) while the pO2 values were decreased (p<0.001) during the pneumoperitoneum and post-operative period as compared to the post-intubation period. During pneumoperitoneum, Ppeak values were increased while compliance values were decreased. Conclusion: Lung US can be used in the diagnosis of atelectasis in obese patients. Atelectasis is seen at a high rate in patients undergoing laparoscopic bariatric surgery.