This study aims to understand the impact on parents of having a child with an undiagnosed medical condition and the factors that contribute to their adaptation. Rare and undiagnosed conditions are often chronic and disabling, with symptoms affecting different organ systems at various levels of severity. Perhaps the most challenging feature of an undiagnosed medical condition that has lasted two or more years, however, is its characteristic uncertainty. In the absence of a diagnosis, health care professionals can provide only limited treatment and prognostic information. It is not well understood how individuals cope with and adapt to chronic uncertainty, and the factors that influence this process. To design future interventions, descriptive studies are needed to reveal predictors that can be manipulated to improve outcomes. In this study, Lazarus and Folkman's Transactional Model of Stress and Coping provides a framework to examine coping and adaptation in the parents of children who have had a chronic, undiagnosed medical condition for two or more years. A cross-sectional research design using a mixed methods survey will be used to examine the relationships among appraisals (perceptions of uncertainty and perceived personal control), time elapsed since parents first realized their child was sick, coping and adaptation. Parents will be recruited from web-based support networks for parents of undiagnosed children via website postings, email listservs and printed newsletter postings. Participants will have the option to complete an online or paper version of the questionnaire. The main outcome variable is adaptation to living with one's child's undiagnosed medical condition.