AbstractAims and ObjectivesExplore families' experiences when being approached for organ donation authorisation after brainstem death.BackgroundThe complexities of potential organ donor families' experiences include challenges related to emotional distress, coping with the loss and the organ donation decision‐making process, and support needed. A lack of conceptual clarity was found concerning families' experiences when being approached for organ donation authorisation, which guided the study.DesignConstructivist grounded theory.MethodsSeventy‐one participants, including healthcare professionals and families, were recruited from two large hospitals in Chile between 2017 and 2019. Field notes, documents (n = 80), interviews (n = 27) and focus groups (n = 14) were collected and analysed following Charmaz's constructivist grounded theory principles and practices until theoretical saturation was reached. The study is reported using the COREQ checklist.ResultsA third type of ambiguous loss of bereaved families' experience was developed as a fourfold process: (1) impending loss, (2) confirming loss, (3) ambiguous loss and organ donation decision‐making and (4) organ donation as a third type of ambiguous loss. This grounded theory expands the concepts of ambiguous loss by Boss, dying by Glaser and Strauss and grief by Brinkmann, enabling explanation of families' experiences.ConclusionFamilies of potential organ donors develop a highly complex grieving process, which may play a significant role in the organ donation decision‐making process. Ambiguity is embedded in how donor families reframe the existence of the donor through the act of giving life.Relevance to clinical practiceThe findings shed light on families' experiences on the organ donation process after brainstem death. The study can be used in nursing practice, education and to inform policy nationally and globally, mainly due to the current focus on quantitative measures and legislative changes fostering individual decision‐making.Patient or Public ContributionFamilies contributed through their first‐hand experiences of the organ donation process.