Background and purpose:The prevalence of Huntington disease (HD) has increased over time; however, there is a lack of up-to-date evidence documenting the economic burden of HD by disease stage. This study provides an estimate of the annual direct medical, nonmedical, and indirect costs associated with HD from participants in the Huntington's Disease Burden of Illness (HDBOI) study in five European countries and the USA. Methods:The HDBOI is a retrospective, cross-sectional study. Data collection was conducted between September 2020 and May 2021. Participants were recruited by their HD-treating physicians and categorized as early stage (ES), mid stage (MS), or advanced stage (AS) HD. Data were collected via three questionnaires: a case report form, completed by physicians who collected health care resource use associated with HD to compute direct medical cost, and optional patient and caregiver questionnaires, which