The aim of this study was to identify risk factors associated with postoperative pulmonary complications. The influence of the anaesthetic technique was evaluated (i.e. general contra regional anaesthesia and long contra intermediately acting muscle relaxants (pancuronium and atracurium)) taking into account the patient's age, the presence or absence of chronic obstructive lung disease (preoperative risk factors), the type of surgery and the duration of anaesthesia (perioperative risk factors). Seven thousand and twenty-nine patients undergoing abdominal, urological, gynaecological or orthopaedic surgery were included in the study. A total of 290 patients (4.1%) suffered from one or more postoperative pulmonary complications. Six thousand and sixty-two patients received general anaesthesia and 4.5% of these had postoperative pulmonary complications. Of the patients admitted to major surgery receiving pancuronium, 12.7% (135/1062) developed postoperative pulmonary complications, compared to only 5.1% (23/449) receiving atracurium (P < 0.05). When stratified for type of surgery and duration of anaesthesia, conventional statistics showed no difference between pancuronium and atracurium as regard postoperative pulmonary complications. However, a logistic regression analysis indicated that long-lasting procedures involving pancuronium entailed a higher risk of postoperative pulmonary complications than did other procedures. In patients having regional anaesthesia, only 1.9% (18/967) developed postoperative pulmonary complications (P < 0.05 compared to general anaesthesia). However, when stratified for type of surgery there was a significantly higher incidence of postoperative pulmonary complications only in patients undergoing major orthopaedic surgery under general anaesthesia, 11.5% compared to 3.6% in patients given a regional anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)