The accuracy of the modified Alvarado score was assessed prospectively in the preoperative diagnosis of acute appendicitis in children. A consecutive series of 118 patients (54 boys, 64 girls) with acute abdominal pain was studied prospectively over a 6 month period. Appendicitis was confirmed in 38 of 43 children undergoing appendicectomy, giving a false-positive appendicectomy rate of 11.6%. No child under active observation was subsequently found to have a perforated appendix. The overall sensitivity of a modified Alvarado score of > or = 7 was 76.3% and its specificity was 78.8%. Current clinical practice is more accurate than the modified Alvarado score in the diagnosis of acute appendicitis in children.