PURPOSE: Recently, randomized controlled trials have reported that conservative therapy can be a treatment option in patients with noncomplicated appendicitis. However, preoperative diagnosis of noncomplicated appendicitis is difficult. In this study, we determined predictive factors to distinguish patients with noncomplicated appendicitis from those with complicated appendicitis. METHODS: A total of 351 patients who underwent surgical treatment for acute appendicitis from January 2011 to December 2012 were included in this study. We classified patients into noncomplicated or complicated appendicitis groups based on the findings of abdominal computed tomography and pathology. We performed a retrospective analysis to find factors that could be used to discriminate between noncomplicated and complicated appendicitis. RESULTS: The mean age of the patients in the complicated appendicitis group (54.5 years) was higher than that of the patients in the noncomplicated appendicitis group (40.2 years) (P < 0.001), but the male-to-female ratios were similar. In the univariate analysis, the appendicocecal junction's diameter, appendiceal maximal diameter, appendiceal wall enhancement, periappendiceal fat infiltration, ascites, abscesses, neutrophil proportion, C-reactive protein (CRP), aspartate aminotransferase, and total bilirubin were statistically significant factors. However, in the multivariate analysis, the appendiceal maximal diameter (P = 0.018; odds ratio [OR], 1.129), periappendiceal fat infiltration (P = 0.025; OR, 5.778), ascites (P = 0.038; OR, 2.902), and CRP (P < 0.001; OR, 1.368) were statistically significant. CONCLUSION: Several factors can be used to distinguish between noncomplicated and complicated appendicitis. Using these factors, we could more accurately distinguish patients with noncomplicated appendicitis from those with complicated appendicitis.