Background The catchment area of REGISTRY study sites in Europe varies from country to country. Also the distances that an HD family member travels for visiting an HD professional and/or for participation into REGISTRY differ.

Aims To better understand the catchment area of REGISTRY sites, to identify regions within a country that have low recruitment into the study, and to develop strategies to improve recruitment of participants from those underrepresented regions.

Methods Data was collected in collaboration with EHDN site staff and Language Area Coordinators respecting participant's anonymity. Data were collected for the total number of participants per study site, place of residence (closest town/city) and population figures for each city or town and county. All REGISTRY sites and catchment area data were mapped.

Outcome The catchment area data showed significant variability in recruitment across regions. This was likely to be due to a number of factors, such as proximity and ease of access to the study sites, characteristics of the centre, the availability specialist care services for HD as well as established national HD networks (eg France, Norway, Sweden and the UK).

Conclusions The catchment area of REGISTRY study sites varies significantly between countries and within countries and can be attributed to a number of national and site specific reasons. The catchment data have enabled strategic planning to promote and sustain the involvement of HD family members from regions that are currently underrepresented in REGISTRY.