Acute appendicitis is one of the most common diseases of young people that requires emergency operation. This is especially true for those age 10 years old and older. However, the numbers of cases of appendicitis are increasing in both the young and the elderly. The main purpose of this study is to understand the clinical features of acute appendicitis in children and elderly patients. We retrospectively compared clinical characteristics in 4 groups of patients who underwent appendectomy in our hospital. There were 16 patients in the pre-school age group, 9 were males and 7 females. The total number of patients in the juvenile group were 287, 156 were males and 131 females. The total numbers of patients in the adult group were 794, 436 were males and 358 females. The numbers of elderly patients were 189, 91 were males and 98 females. Complicated appendicitis was found in 15 patients (93.7 %) in the pre-school age group, 79 patients (27.5 %) in the juvenile group, 332 patients (41.8 %) in the adult group, and 96 patients (50.7 %) in the elderly group. Four patients (40 %) had generalized panperitonitis in the pre-school group. The occurrence of perforated appendicitis was the highest in the pre-school age group and the lowest in the juvenile group. Since generalized panperitonitis has a higher incidence in the pre-school age group, prudent and careful diagnosis and treatment are required for the pre-school age group.