BACKGROUND: Little evidence indicates that changing a patient's body position to the Trendelenburg (head lower than feet) or the modified Trendelenburg (only the legs elevated) position significantly improves blood pressure or low cardiac output. This intervention is still used and is often the first measure implemented for treatment of hypotension. OBJECTIVES: The purpose of this research was to assess the degree of use of Trendelenburg positions by critical care nurses, the clinical uses of these positions, and the sources of knowledge and beliefs of nurses about the efficacy of the positions. METHOD: A survey was mailed to 1000 nurses whose names were randomly selected from the membership list of the American Association of Critical-Care Nurses. RESULTS: The return rate was 49.4%. Ninety-nine percent of the respondents had used the Trendelenburg position, and 80% had used the modified Trendelenburg position, mostly for treatment of hypotension. Most used this intervention as an independent nursing action, and most learned about these positions from their nursing education, nurse colleagues, supervisors, and physicians. The Trendelenburg position was used for many nonemergent reasons; the most frequent use was for insertion of central IV catheters. Although 80% of the respondents believed that use of the Trendelenburg position improves hypotension almost always or sometimes, many respondents recognized several adverse effects associated with use of this position. DISCUSSION AND CONCLUSIONS: The results provide evidence that tradition-based therapy still underlies some interventions used in the care of critically ill patients and that some nurses may be relying on an outdated knowledge base that is not supported by the current literature.