A valid, reliable measure of family caregivers’ knowledge about delirium was not located in the literature; such an instrument is essential to assess learning needs and outcomes of education provided. The purpose of the current study was to (a) develop a family Caregiver Delirium Knowledge Questionnaire (CDKQ) based on the Symptom Interpretation Model; and (b) establish validity and reliability of the measure. The 19-item CDKQ was developed and administered to 164 family caregivers for community-dwelling older adults. Descriptive statistics were examined for all variables. Psychometric testing included confirmatory factor analysis, item-to-total correlations, and internal consistency reliability. A three-factor model provided the best fit for the data. The findings support initial validity and reliability of the CDKQ with family caregivers. Although the CDKQ was developed for use with family caregivers, it has potential for use with other caregivers, such as home health aides.