When ventilatory support becomes necessary in patients with acute respiratory failure, there is an associated increase in complications. We reviewed the charts of acute respiratory failure patients with the ventilatory support retrospectively who were admitted to the General Intensive Care Unit, Yonsei University College of Medicine, Seoul, Korea for the 6 months period, from March through August, 1990. The data included incidence of complications, morbidity and mortality, and reasons for and the duration of the ventilatory support. Of 269 patients receiving the ventilatory support, 107 patients (39.8%) developed 159 complications including alveolar hyperventilation (56 times), premature extubation (20 times) and right bronchial intubation (16 times). A single complication was associated with mortality rate of 19.5%, while with two or more complications, mortality rate was 60%, giving an average mortality rate of 29% when the complications were identified. The highest incidence of complications was in patients with multiple organ failure (80%). The highest mortality rate (50%) occurred in patients with heart failure. Patients with the ventilatory support less than one day had 23% incidence of complications and 2.7% mortality, while those with support for more than one month, these figures were 90.0% and 40.0% respectively (p<0.05).