The incidence of acute appendicitis was studied in a well defined population. Results from 971 appendectomies performed on suspicion of appendicitis, comprising 955 primary and 16 interval operations, were collected over a four-year period. Appendicitis was diagnosed in 657 cases and the mean yearly incidence was 1.16 per thousand. The incidence in males was 1.33 per thousand versus 0.99 for females. The difference was statistically significant (p = 0.0002). The mean yearly incidences of appendectomies were 1.72 per thousand for males and 1.71 for females. The highest incidences of both appendicitis and appendectomies for both sexes occurred in the second decade of life (2.34/1,000 and 3.63/1,000 per annum, respectively). Slight increases in the frequencies of appendicitis and appendectomies were noticed in the very old patients. There were no differences between the results of this study and other recent comparable reports. Compared with earlier studies there was no marked decline in the incidence of appendicitis.