Objective: This exploratory, pilot study aimed to investigate motivations and reflections of participants who had provided epidemiological information, blood samples and access to clinical records and data in a large genetic epidemiological study of endometriosis, a common multifactorial disorder affecting women. We also aimed to explore understanding of complex genetic or multifactorial conditions in general. Methods: In-depth interviews were conducted with 16 endometriosis study participants with diverse characteristics. Results: Interviewees generally described their participation in the genetic study using altruistic frameworks of reference. Themes that emerged included unquestioning willingness and consent to participate, little concern about privacy issues, desire for more information from the researchers about the condition rather than scientific progress, the benefits of research participation to family communication, and differing ideas about genetic infl uences on endometriosis. Specific features of endometriosis also influenced reflections on research participation experience. Conclusions: As increasing numbers of individuals and families in the community become involved in genetic epidemiological studies of common diseases, more extensive research will be needed to better understand their expectations with a view to improving researchers’ communications with study participants.