Advance care planning in young-onset dementia largely remains a blind spot within current literature. This study aimed to explore the engagement in and the conceptualization of advance care planning from the perspective of family caregivers of persons with young-onset dementia and to identify potential similarities and differences in this area between American and Belgian persons with young-onset dementia and their family caregivers. An exploratory qualitative study. We purposively sampled adult family caregivers of persons with young-onset dementia; our respondents were 13 American and 15 Belgian caregivers with varying familial relationships to the patient. We conducted 28 semi-structured interviews, using the same interview guide for American and Belgian respondents. Verbatim transcripts were analysed through the method of constant comparative analysis. Important similarities between American and Belgian respondents were restricted knowledge of advance care planning, limited communication about advance directives, and their recommendation for professionals to timely initiate advance care planning. Major differences were attention paid to those end-of-life decisions depicted in the legislature of their respective countries, American caregivers placed higher emphasis on financial planning than their Belgian peers, and, in the case of consulting professionals for advance directives, American caregivers turned to lawyers, whereas Belgian caregivers relied on physicians. Specific nuances and challenges in terms of advance care planning in young-onset dementia arise from a particular societal and legal context on the one hand, and from patients' and caregivers' younger age on the other. Professionals' awareness of and responsiveness to these specificities could facilitate the advance care planning process. Based on our interpretation of results, several recommendations for practice and policy are made.