BACKGROUND: Family-administered delirium detection tools may serve as valuable diagnostic adjuncts because family caregivers may be better able than providers to detect changes in patient cognition and behaviour from pre-illness levels of functioning. The aim of this pilot study was to assess the feasibility and acceptability of family-administered tools to detect delirium in critically ill patients. METHODS: In this single-centre pilot tool validation study conducted in August and September 2017, eligible family caregivers used the Family Confusion Assessment Method (FAM-CAM) and the Sour Seven questionnaire to detect delirium during the patients intensive care unit (ICU) stay. We calculated descriptive statistics for all study variables. Patients and family caregivers were involved as research partners throughout the study. A patient-orient research approach was taken, engaging patients and family caregivers as full partners. RESULTS: Of 141 patients admitted to the ICU, 75 were eligible, of whom 53 were approached; 21 patients (40%), 23/38 family caregivers (60%) and 17/38 dyads (i.e., patient and family caregiver enrolled together) (45%) consented to participate. The most common reason for nonenrolment was refusal by the family, who commonly reported feeling overwhelmed. The completion rate for the FAM-CAM and Sour Seven questionnaire was 74% (17/23). Among 13 dyads, family caregivers detected delirium in 5 patients (38%) using the FAM-CAM, and delirium or possible delirium in 8 patients (62%) using the Sour Seven questionnaire, whereas trained research assistants detected delirium in 8 patients (62%) using the Confusion Assessment Method for the Intensive Care Unit 7 and the Richmond Agitation-Sedation Scale (κ coefficient for agreement between the former and the FAM-CAM and Sour Seven questionnaire 0.62 and 0.85, respectively). INTERPRETATION: Administration of the FAM-CAM and Sour Seven questionnaire by family caregivers to detect delirium in the ICU is feasible and acceptable, although, as with most family engagement strategies, it was not desired by all. Results from this pilot study support a definitive study with a larger sample to enable calculation of inferential statistics, but additional recruitment strategies are necessary to improve the response rate. Trial registration: Clinicaltrials.gov, no. NCT03379129.