The aim of this prospective study was to evaluate the frequency of postoperative fluid collection after laparoscopic appendectomy in patients with normal postoperative development. Twenty-eight patients were included. The surgical technique, histological data, and postoperative development during the first postoperative month were recorded. A sonographic analysis was performed on the 5th postoperative day by a radiologist who was not aware of the histological and surgical data. Ten cases of fluid collection were found (37%). The frequency was higher in cases of suppurated appendicitis and significantly higher with associated periappendicitis. Peritoneal irrigation or retrocecal dissection did not influence the occurrence of fluid collection. Postoperative serous fluid collection occurs with a high frequency after laparoscopic appendectomies, and one must be careful in interpreting sonographic analyses in looking for deep abscesses in patients with difficult postoperative development.