Correlation of APACHE II score, drainage technique and outcome in postoperative intra-abdominal abscess. The APACHE II Score was used to stratify retrospectively severity of illness in 91 patients postoperatively undergoing drainage of intra-abdominal abscesses. The method of initial abscess drainage (percutaneous or operative) was selected by the attending physician. The two groups of patients, those whose initial drainage was performed percutaneously versus operatively were similar with respect to age, sex, abscess location and, most importantly, severity of illness as assessed by the APACHE II score calculated on the day of their abscess drainage. Over-all, the mortality rate was 29 per cent (26 of 91 patients). Only 1.7 per cent of the patients with an APACHE II score of less than 15 died compared with 78 per cent when APACHE II was equal to or more than 15 (p less than 0.0001). Only 8 per cent of patients with APACHE II equal to or more than 15 undergoing percutaneous drainage survived compared with 30 per cent of patients who underwent surgical drainage procedures. While chi-square analysis demonstrated independence between outcome and drainage technique, outcome was dependent upon severity of illness (p less than 0.0005). Paradoxically, despite the attractiveness of a percutaneous technique for abscess drainage in the most ill patients, in this series, a better, although not statistically improved, chance for survival was noted with surgical treatment. We recommend that an objective severity scoring system be used whenever assessing results of treatment of intraabdominal infection and that surgical treatment not be avoided because the patient is considered to be too ill. 