Background: Laparotomy causes a significant reduction of pulmonary function, and atelectasis and pneumonia occur after elective conventional colorectal resections.Objective: To evaluate the hypothesis that pulmonary function is less restricted after laparoscopic than after conventional colorectal resection.Design: A randomized clinical trial.Setting: The surgical department of an academic medical center.Patients: Sixty patients underwent laparoscopic (n = 30) or conventional (n = 30) resection of colorectal tumors. The 2 groups did not differ significantly in age, sex, localization or stage of tumor, or preoperative pulmonary function.Main Outcome Measures: Forced vital capacity, forced expiratory volume in 1 second, peak expiratory flow, midexpiratory phase of forced expiratory flow, and oxygen saturation of arterial blood.