The complexity of patients cared for in modern ICUs, along with continuing advances in the technology of critical care and the escalating costs associated with providing that care, have been motivating factors for critical care practitioner to identify and implement 'best' medical practices. Individual best practices are often determined based on their association with improvements in patient outcomes, increased efficiency and cost-effectiveness of medical care, or both. These practices should ideally be determined based on sound medical evidence obtained from rigorously performed clinical trials, the most rigorous being randomized controlled trials. However, such trials have often not been performed for many aspects of critical care medicine. Outcomes research is an emerging field which attempts, in part, to use variations in medical practices, as well as formal scientific investigations, to identify important associations between specific medical practices and clinical outcomes. This review focuses on two areas of mechanical ventilation, acute respiratory distress syndrome (ARDS) and weaning, to illustrate how outcomes research can be employed to facilitate decision making in the management of patients with respiratory failure.