This article discusses the conceptualization and measurement of family-nurse relationships in pediatric intensive care unit (PICU) from the perspective of family systems and boundaries. The 14 items for the Family-Nurse Boundary Ambiguity Scale for PICU (FNBAS-PICU) were developed from a qualitative study. Nurse panels established face and content validity. Parents (156) from four PICUs participated in reliability estimates (Cronbach's alpha =. 81) and validity testing with measures of illness uncertainty and role alteration stress. Principal components analysis confirmed the conceptual intent of the FNBAS-PICU.