OBJECTIVE: To compare the survival and clinical outcomes of critically ill patients treated with the use of a pulmonary artery catheter (PAC) to those treated without the use of a PAC. DESIGN: Prospective, randomised, controlled, clinical trial from October 1997 to February 1999. SETTING: Adult intensive care unit at a large teaching hospital. PATIENTS: Two hundred one critically ill patients were randomised either to a PAC group ( n=95) or the control group ( n=106). One patient in the control group was withdrawn from the study and five patients in the PAC group did not receive a PAC. All participants were available for follow-up. INTERVENTIONS: Participants were assigned to be managed either with the use of a PAC (PAC group) or without the use of a PAC (control group). MAIN OUTCOME MEASURES: Survival to 28 days, intensive care and hospital length of stay and organ dysfunction were compared on an intention-to-treat basis and also on a subgroup basis for those participants who successfully received a PAC. RESULTS There was no significant difference in mortality between the PAC group [46/95 (47.9%)] and the control group [50/106 (47.6)] (95% confidence intervals for the difference -13 to 14%, p>0.99). The mortality for participants who had management decisions based on information derived from a PAC was 41/91 (45%, 95% confidence intervals -11 to 16%, p=0.77). The PAC group had significantly more fluids in the first 24 h (4953 (3140, 7000) versus 4292 (2535, 6049) ml) and an increased incidence of renal failure (35 versus 20% of patients at day 3 post randomisation p<0.05) and thrombocytopenia ( p<0.03). CONCLUSIONS: These results suggest that the PAC is not associated with an increased mortality.