In patients with right lower quadrant pain, the total white cell count is an unreliable predictor of appendicitis. It has been reported that the lymphocyte count can fall in acute appendicitis. This study was undertaken to investigate whether the neutrophil:lymphocyte ratio is a more sensitive indicator than the total leucocyte count. A retrospective study was performed of patients undergoing appendectomy for suspected appendicitis over a 2-year period. A total of 402 patients were identified; histopathology confirmed appendicitis in 367 (91%). Other significant pathology was found in 13 (3.2%). Twenty-two (5.5%) had a histologically normal appendix and recovered uneventfully with no other diagnosis being made. A total of 298 (79%) patients with appendicitis had an elevated preoperative total white cell count. The neutrophil:lymphocyte ratio was calculated for each patient. Using an upper limit of 3.5:1, it was found that 324 (88%) of patients with appendicitis had a ratio equal to or greater than this value. This was significantly different from the proportion with a raised total leucocyte count (P = 0.001). We suggest that the simple calculation of the neutrophil:lymphocyte ratio may provide a parameter that is more sensitive than the total leucocyte count in the prediction of appendicitis.