This study was designed to determine the values of C-Reactive Protein measurements (an acute phase reactant, CRP) and leucocyte counts in prevention of negative appendectomies. Despite improvements in diagnostic methods, negative appendectomy rates still remain between 10-30% in acute appendicitis. Cost-effective and easily applicable diagnostic methods with prompt results are required to reduce negative appendectomy rates. In this prospective study, one hundred twenty-six patients were operated on for initial diagnosis of acute appendicitis between July 1999 and July 2000. CRP and leucocyte count were measured in all cases. The data of the outcomes of clinic and pathological findings were analyzed statistically. Among the 126 study patients, 71 (56.3%) were male and 55 (43.7%) were female. 79 (62.6%) cases had noncomplicated appendicitis, 27 (21.4%) cases had complicated appendicitis and 20 (15.8%) cases had negative appendectomy. The mean CRP level was significantly higher (p < 0.001) in patients with complicated acute appendicitis than in those with noncomplicated acute appendicitis and in those with negative appendectomy. The mean leucocyte count was significantly lower (p < 0.001) in patient with negative appendectomy than in those with noncomplicated appendicitis and in those with complicated appendicitis. Although CRP increases with inflammation, it increases markedly after the occurrence of complication. The increase in leucocyte count is early sign of appendix inflammation. CRP measurements or leucocyte counts are not effective alone to prevent negative appendectomies.