In a prospective trial comprising 202 patients operated on because of suspicion of acute appendicitis, the diagnostic accuracy was 70 percent based on histologic examination of all removed appendices. The diagnostic accuracy was lowest in women less than 50 years old and in young patients (aged 20 years or less), being about 60 percent in both of these groups. The reasons were gynecologic disorders and uncharacteristic abdominal pains, respectively. Twenty-three of the 142 patients with acute appendicitis had perforation (16 percent). The frequency of perforation was significantly higher in patients more than 50 years old. Postoperative complications were seen in 11 percent of the patients. There was no significant difference in the frequency of complications in patients with a normal appendix and no other surgical abdominal disorder and patients with nonperforated appendicitis. However, there was a statistically significant difference between these two groups and the group with perforated appendicitis. In the latter group, postoperative complications occurred in 39 percent of the patients as opposed to 4 percent and 8 percent, respectively, in the former groups.