Background: The outcome oí' mechanically ventilated patients can be inñuenced byfactors such as the indication of mechanical ventilation (MV) and ventilator parameters. Aim: To describe the characterístics of patients receiving MV in Chilean critical care uníts. Material and methods: Prospective cohort of consecutive adult patients admitted to 19 intensive care uníts ([CU) from 9 Chilean cities who received MV for more than 12 hours between September lst, 2003, and September 28th, 2003. Demographic data, severity of illness, reason for the initiation of MV, ventilation modes and settings as well as weaning strategies were registered at the initiation and then, daily throughout the course of MV for up to 28 days. ¡CU and hospital mortality were recorded. Resulte: Of 588 patients admitted, 156 (26.5%) received MV (57% males). Mean age and Simplified Acute Physiology Score-II (SAPSII) were 54.6±18years and 40.6±16.4 points respectively The most common indications for MV were acute respiratory failure (71.1%) and coma (22.4%). Assist-control mode (71.6%) and synchronized intermittent mandatory ventilation (SIMV) (14,2%) were the most frequently used. T-tube was the main weaning strategy. Mean duration of MV and length of stay in ICU were 7.8±8.7 and 11.1± 14 days respectively. OverallICUmortality was 33.9% (53patients). The main factors independently associated with increased mortality were (1) SAPS II ≥ 60 points (Odds Patio (OR), 10.5; 95% CI, 1.04-106.85) and (2) plateaupressure ≥ 30 cm Hfi atsecond day (OR, 3.9; 95% CI, 1.17-12.97). Conclusions: Conditionspresent at the onsetofMVand ventilator management were similar to those reported in the literature. Magnitude ofmultiorgan dysfunction and high plateau pressures are the most important factors associated with mortality).