Although delay in the administration of appropriate antibiotic treatment for ventilator-associated or community-acquired pneumonia is associated with increased hospital mortality, impact of appropriateness of initial antibiotic therapy on outcome of postoperative pneumonia has been poorly investigated. Of 7,275 patients who had undergone intraabdominal surgery under general anesthesia between January 1998 and December 2005, we compiled a list of 101 patients with microbiologically confirmed postoperative pneumonia. We analyzed the influence of the appropriateness of initial antibiotic therapy on outcome of postoperative pneumonia using logistic regression analysis. Among the patients with postoperative pneumonia, about a half received inadequate initial antimicrobial therapy. As well as the presence of concomitant intraabdominal abscess [odds ratio (OR) = 28.83), prolonged duration of anesthesia at surgery (OR = 22.41), and the isolation of methicillin-resistant Staphylococcus aureus (OR = 8.86), inadequate initial antibiotic therapy was a determinant of death from postoperative pneumonia (OR = 16.75). The outcomes of patients with postoperative pneumonia could be improved by avoiding concomitant intraabdominal abscess, reducing surgical insult, and administering appropriate antimicrobial agents.