Purpose: Studies into the preferences of patients and relatives regarding informed consent for intensive care unit (ICU) research are ongoing. We investigated the impact of a study's invasiveness on the choice of who should give consent and on the modalities of informed consent. Methods: At ICU discharge, randomized pairs of patients and relatives were asked to answer a questionnaire about informed consent for research. One group received a vignette of a noninvasive study; the other, of an invasive study. Each study comprised two scenarios, featuring either a conscious or unconscious patient. Multivariate models assessed independent factors related to their preferences. Results: A total of 185 patients (40%) and 125 relatives (68%) responded. The invasiveness of a study had no impact on which people were chosen to give consent. This increased the desire to get more than one person to give consent and decreased the acceptance of deferred or two-step consent. Up to 31% of both patients and relatives chose people other than the patient himself to give consent, even when the patient was conscious. A range of 3 to 17% of the respondents reported that they would accept a waiving of consent. Younger respondents and individuals feeling coerced into study participation wanted to be the decision makers. Conclusions: Study invasiveness had no impact on patients' and relatives' preferences about who should give consent. Many patients and relatives were reluctant to give consent alone. Deferred and two-step consent were less acceptable for the invasive study. Further work should investigate whether sharing the burden of informed consent with a second person facilitates participation in ICU researc
