PURPOSE: Laparoscopic appendectomy has recently been performed more frequently than open appendectomy because of its advantages. Yet laparoscopic appendectomy has the risk of converting to open appendectomy. We evaluated the preoperative evaluation factors that can influence the rate of conversion to open appendectomy. METHODS: For the 255 patients admitted to our hospital, we reviewed their medical history, their clinical and laboratory examination etc. and the final diagnosis was made by CT scan. The preoperative characteristics of the patients who underwent laparoscopic appendectomy and the patients who were converted to open appendectomy were compared using univariate and multivariate analysis. RESULTS: Out of 255 patients who underwent laparoscopic appendectomy, 15 patients (5.8%) were converted to open appendectomy. The main reasons were adhesion and periappendiceal abscess formation. Periappendiceal fat infiltration (p=0.030) seen in the CT scan and perforation (p=0.019) were significant risk factors associated with converting to open appendectomy. CONCLUSION: Periappendiceal fat infiltration and perforation seen on preoperative CT scanning are important when considering performing laparoscopic appendectomy. Identifying the potential preoperative factors for conversion may assist surgeons when making decisions concerning the management of patients with appendicitis and for the judicious use of LA.