Introduction: Morbidly obese patients have reduced efficiency of lung ventilation. It could be significantly decreased after bariatric surgery. Aim: The aim of the study was to compare change of respiratory efficiency directly after bariatric surgery performed via laparotomy or laparoscopy. Materials and methods: We used peak expiratory flow (PEF) to estimate efficiency of lung ventilation, which we had measured before the operation and on postoperative days 1 and 3. The patients were divided into 3 study groups: group I qualified for vertical bonded gastroplasty (VBG), group II qualified for laparoscopic vertical bonded gastroplasty (LVBG), group III qualiflied for laparoscopic gastric banding (LAGB). Results: The results of this study are as follows: in group I PEF before operation was 399 1/min, on postoperative day 1 it was 195 1/min, on day 3 it was 282 1/min; in group PEF before operation was 453 1/min, on postoperative day 1 it was 327 1/min, on day 3 it was 410 1/min; in group PEF before operation was 460 1/min, on postoperative day 1 it was 340 1/min, on day 3 it was 430 1/min. Conclusions: Recovery of efficiency of lung ventilation, which was close to values before operation, was on postoperative day 3 after surgery performed via laparoscope. It was not influenced by performing LVBG or LABG, in spite of significant difference in duration of surgery. The values of PEF in patients after open surgery on postoperative day 3 significantly differed from preoperative values (p <0. 05).