BACKGROUND: Little research exists on the role of β-amyloid PET scans as part of Alzheimer's diagnostic tests and documentation of end-of-life preferences for persons with cognitive impairment. The study objectives were to examine the association of amyloid PET scan results (elevated vs. not elevated amyloid levels) and diagnostic category (mild cognitive impairment vs. dementia) with the likelihood of having an advance directive (reported a median of 4.5 months post-scan); to explore perceptions of PET scan results and their influence on planning for the future among persons with cognitive impairment and their care partners. METHODS: Sequential, explanatory mixed-methods design using data from dyads in the CARE-IDEAS study: advance directives as a factor of diagnostic category and scan result using multivariable logistic regression models; thematic analysis of semi-structured interviews with persons with cognitive impairment and care partners to explore how scan results influenced documentation of future healthcare preferences. Participants included 1784 persons with cognitive impairment and care partners from the CARE-IDEAS study, and a subsample of 100 semi-structured telephone interviews. RESULTS: 81.6% of dyads reported an advance directive. Non-Hispanic, White participants had higher rates of advance directives. There was no significant association between having an advance directive and scan results. Qualitative analysis provided insight into perceived urgency to have advance directives, evolving healthcare preferences, and the context of completing advance directives. CONCLUSIONS: Although amyloid PET scans prompted persons with cognitive impairment and care partners to consider progressive cognitive impairment as part of evolving healthcare preferences, we found substantial variability in the perceived urgency of documentation.