Appendiceal malignant tumors among patients with acute appendicitis Background: Acute appendicitis can be the fi rst manifestation of an appendiceal tumor. Aim: To evaluate the incidence of appendiceal tumors among patients operated for acute appendicitis. Material and Methods: All patients operated for acute appendicitis between 1998 and 2008 and whose appendix had a pathological study were included. Survival was calculated using national death register databases. Results: Data from 6.093 patients was analyzed. A malignant tumor was found in 17 patients (0.3%). Eleven patients aged 23 ± 14 years had a carcinoid tumor, that was more commonly located distally, fi ve patients aged 66 ± 18 years had an adenocarcinoma, that was more commonly located proximally, and one patient had a non Hodgkin lymphoma. Curative surgery was carried out in all carcinoid tumors and 40% of adenocarcinomas. No patient had regional lymph node involvement. Five years survival of patients with carcinoid tumors was 100%. Conclusions: The fi nding of malignant tumor among patients with acute appendicitis is uncommon.