Those living without a diagnosis reside in an invisible margin of health and family research. The purpose of this study was to explore illness uncertainty as experienced by women and their families in the United States. I examined illness uncertainty through a feminist ecological interactionist (FEI) approach with three core constructs: interaction, agency, and context. I conducted narrative-focused, semi-structured interviews with 15 women (aged 25-46) and 11 family members (aged 22 to 62) identified by each woman and completed a constant comparative grounded theory analysis. The findings revealed women's lived experiences with symptoms and social support, interactions with the medical system, and agency in the context of such uncertainty. Findings also model a System of Illness Uncertainty that contends that women's experiences with illness uncertainty is an endless process that changes over time. In the System of Illness Uncertainty, women were Doubters, Resisters, Persisters, or Burnouts; all women experienced a paradigm shift regarding the Western health system as a result of their experiences. This research adds to the knowledge base on individuals who occupy spaces between the legitimized, diagnosable ill and the symptom-free healthy. Implications affect not only individuals and their families, but the politics of Western medical establishments. / Ph. D. / Those living without a diagnosis are often outside of health and family research. The purpose of this study was to explore women and their families’ experiences of illness uncertainty (i.e., living without a diagnosis) in the United States. I examined illness uncertainty through a feminist ecological interactionist (FEI) approach guided by three core constructs: interaction, agency, and context. I conducted semi-structured interviews with 15 women (aged 25-46) and 11 family members (aged 22 to 62) identified by each woman and completed a constant comparative grounded theory analysis. The findings revealed women’s lived experiences with symptoms and social support, interactions with the Western health system, and agency in the context of such uncertainty. I put forward a System of Illness Uncertainty that contends that women’s experiences with illness uncertainty is an endless process that changes over time; women were Doubters, Resisters, Persisters, or Burnouts. I argue that all women experienced a shift in thinking about the Western health system as a result of their experiences. This research adds to the knowledge base on individuals who occupy spaces between the legitimized, diagnosable ill and the symptom-free healthy. Implications affect not only individuals and their families, but the politics of Western medical establishments.