Transperitoneal versus extraperitoneal laparoscopic paraaortic lymphadenectomy. Randomized experimental study. Objectives: The objective of this study was to compare the risk of adhesion formation and the site of postoperative adhesions after transperitoneal versus extraperitoneal laparoscopic paraaortic lymphadenectomy. Material and method: A prospective randomized trial was conducted on 66 pigs, submitted to transperitoneal ( n=33) or extraperitoneal ( n=33) laparoscopic paraaortic lymphadenectomy. The efficacy and the intra and postoperative morbidity (adhesion score taking into accoint the number of adhesions and the surface area involved) of each approach were compared. The site of postoperative adhesions in relation to a simulated external irradiation field was determined by a stereolocalization system (Syslav) on 20 pigs. Results: No statistically significant difference was observed between the two techniques in terms of operating time, number of lymph nodes removed, and intra and postoperative morbidity except for lymphoceles and adhesions. No case of lymphocele was observed in the transperitoneal group versus 13 cases (43.33%) in the extraperitoneal group ( P=0.0002). Final total adhesion score was 76% ( n=22) in the transperitoneal group versus 63.33% ( n=19) in the extraperitoneal group. Adhesion score specific to the operative site was 76 % ( n = 21) in the transperitoneal group versus 43.33% ( n=13) in the extraperitoneal group ( P=0.04). A statistically significant difference was observed between the two approaches in terms of final total adhesion score ( P=0.008) or adhesion score specific to the operative site ( P=0.0005). The stereolocalization study showed that almost all adhesions were situated in the paraaortic external irradiation field after transperitoneal laparoscopy, while adhesions were predominantly situated outside this field after extraperitoneal laparoscopy. Conclusions: Extraperitoneal laparoscopy generates significantly fewer adhesions in the paraaortic irradiation field and should have a risk of radiation enteritis less important than transperitoneal laparoscopy.