A prospective study of 110 unselected patients with suspected acute appendicitis comprised ultrasonography and parameters of inflammation--c-reactive protein, white blood cell count, erythrocyte sedimentation rate and Yersinia antibody titer. The results were compared with the initial clinical diagnosis. Acute appendicitis was confirmed in 28 cases (prevalence 25.4%). The negative laparotomy rate was 11.4% and the appendiceal perforation rate 10.7% Clinical judgment and ultrasonography were statistically highly significant as predictors of acute appendicitis, whereas the indications given by c-reactive protein and white blood cell count did not reach statistical significance.