Background: Admitting an older adult to a nursing home involves significant adjustment efforts by the family. Our goal was to prepare an assessment instrument for this, given that there was none to date. Method: Participants—134 relatives from different nursing homes in the region of Murcia. Instruments—structured interview for socio-demographic information, satisfaction with the nursing home, well-being and health self-assessment, Radloff’s Depression Questionnaire (CES-D), and the first version of CAFIAR. Results: A 15-item instrument with three factors was obtained: Factor 1 (Unease due to admitting an older adult to a nursing home), Factor 2 (Relief), and Factor 3 (Nostalgia and concern for the older adult), in addition to a general adjustment index, with a Cronbach’s alpha of 0.74. The general adjustment index and the subscales that demonstrate poor adjustment were significantly correlated with depression and a worse health self-assessment, while the Relief subscale, which indicates better adjustment, was significantly correlated with well-being and a positive health self-assessment. Conclusions: The family adjustment in admitting an older adult to a nursing home questionnaire (CAFIAR) has adequate psychometric properties to assess family adaptation in admitting an older adult to an institution.