One thousand cases of appendicitis seen from 1963 to 1973 were reviewed. The overall negative appendectomy rate was 20%, but in women between ages 20 and 40 it exceeded 40%. Two thirds of the negative appendectomies were due to nonsurgical lesions. Mesenteric adenitis, gastroenteritis, and abdominal pain of unknown cause accounted for one third of the errors in females and two thirds in males. These diseases were best distinguished from appendicitis on the basis of temperature and white blood cell count. The remainder of the errors in females were due to pelvic inflammatory disease or other gynecologic diagnosis and were best distinguished from appendicitis on the basis of history and physical findings. The rate of perforation was 21% overall. The incidence of wound infection was 8.5%. Use of systemic antibiotics did not affect the wound infection rate.