PURPOSE: To estimate the prevalence of acute appendicitis and the relationship between pregnancy and acute appendicitis among South Korean women in 2009. METHODS: This was a cross-sectional study over 1 year period using a national registry data. We analyzed a national patient sample (n = 1,116,040) from a database complied by the South Korean National Health Insurance in 2009. RESULTS: We identified 15,974 cases of acute appendicitis from 2009. The prevalence rate of acute appendicitis was 228 +/- 2 per 100,000 persons. The prevalence in men was higher than in women. The peak prevalence of the disease in both genders occurred in patients aged 10 to 14 years. After that, prevalence declined with age. The prevalence of acute appendicitis in women aged 20 to 39 years was negatively associated with age and pregnancy (P < 0.001) but was not associated with socioeconomic status. The prevalence of perforated appendicitis cases by age is represented by a U-shaped curve. The prevalence was highest in people less than five years of age and in people older than 60 years. CONCLUSION: We found that the prevalence of acute appendicitis decreased with increasing age after early teens, and that the prevalence of acute appendicitis in pregnant women was lower than in nonpregnant women.