The type and frequency of complications after open Roux-en-Y gastric bypass (GBP) have changed with the development of laparoscopic technique. The number of laparoscopic GBP cases performed in the United States has increased dramatically during the past several years. We compared the type and frequency of complications after laparoscopic and open GBP. We searched MEDLINE from January 1, 1994, through December 31, 2002, using the keywords morbid obesity, laparoscopy, bariatric surgery, and gastric bypass. We selected studies on laparoscopic or open GBP with more than 50 patients and published in the English language for analysis. We excluded studies with reoperative Roux-en-Y GBP cases or other bariatric procedures. The type and frequency of postoperative complications were recorded from each study. We used chi2 and Fisher exact tests to determine statistical significance. Ten laparoscopic GBP studies with 3464 patients and 8 open GBP studies with 2771 patients were considered. The mean of the reported average age for patients undergoing laparoscopic GBP was 41 years compared with 43 years for open GBP. The mean percentages of female patients were 87% for laparoscopic GBP and 82% for open GBP; the mean reported average body mass index (calculated as weight in kilograms divided by the square of height in meters), 48.7 and 49.5, respectively. Compared with open GBP, laparoscopic GBP was associated with a decrease in the frequency of iatrogenic splenectomy, wound infection, incisional hernia, and mortality; however, there was an increase in the frequency of early and late bowel obstruction, gastrointestinal tract hemorrhage, and stomal stenosis. There were no significant differences in the frequency of anastomotic leak, pulmonary embolism, or pneumonia. The type and frequency of postoperative complications after laparoscopic and open GBP are different. Certain complications increase with laparoscopic GBP, probably owing to the learning curve of this complex procedure, whereas other complications decrease because of the advantages of the smaller access incision.