Drawing on literature relevant to the impact of sibling death, the authors examined the invisible loss of siblings never known. This article presents findings of a phenomenological study of 15 adult siblings who "storied" the psychological presence and power of a deceased infant sibling never known but who acted as memory keepers for their unknown sibling. Transcriptions of the 15 interviews were analyzed using NVivo software to support development of thematic categories. The initial 29 subthemes were collapsed into 3 overarching themes of personal loss/unacknowledged loss, continuing bonds/memory keeping, and sense-making. The participants' experiences reflect support for unaddressed and unacknowledged loss for the phenomenon of loss of an unknown sibling. The retrospective narratives echo their perceived roles as memory keepers of their unknown siblings. For many participants, the research process itself was the first recognition of a sense of loss. (Contains 1 table.)