 The values of laboratory examinations which are useful for the diagnoses of acute appendicitis are white blood cell count WBC, C-reactive protein CRP and erythrocyte blood sedimentation rate ESR. Another laboratory value which has recently received considerable attention for the early diagnosis of bacterial infection and sepsis is pro-calcitonin PCT. In recent studies it has been clearly shown that PCT is one of the most important biochemical indicators which closely correlates with the severity of inflammatory host response to microbial infections. Aim of this open, prospective study is therefore to investigate if PCT has an accurate diagnostic value for the diagnosis of acute appendicitis. 