Infectious complications such as wound infection and intra-abdominal abscess are rarely fatal, but perplexing to both patients and surgeons, and still remain asserious problem after appendectomy in about 5% of the patients. To be helpful to reduce post-appendectomy complications, authors retrospectively analyzed 229 cases of appendectomy performed during the period of one year, from January 1 through December 31, 1995, to find out contributing factors to the post-appendectomy infectious complications such as wound infection or intra-abdominal abscess. The results were as follows. 1) Infectious complications are more common in patients with four or more days of symptom. 2) Infectious complications are more common in patients with complicated appendicitis such as gangrenous or perforated appendicitis. 3) Preoperative antibiotics are helpful to prevent infectious complications in cases of complicated appendicitis. 4) There is no difference in the incidence of infectious complications between the immediate operations and overnight delayed operations in patients who were admitted in the late evening or at night. 5) There is no difference in the incidence of infectious complications between operators: staff surgeons who exclusively operated on patients with complicated appendicitis and residents(with or without supervision of staff surgeons) who mostly operated on patients with simple appendicitis. This means technical superiority has its role in preventing infectious complications. Early diagnosis and operation before the gangrenous change or perforation are warranted. Preoperative antibiotics are effective in cases of complicated appendicitis, but not in cases of simple appendicitis. But the lack of objective criteria to decide complicated appendicitis before the operation remains problem, and prospective study to solve this problem is needed. Technical perfectness is required to protect the wound and to remove the appendix without contamination. Preventive measures are also important to prevent the infectious complications in cases of inevitably contaminated wounds or inta-abdominal spaces.