Objective: We aimed to develop a parent-reported outcome measure for febrile infants 60 days or younger evaluated in the emergency department. Methods: We conducted a 3-part study: (1) individual, semistructured interviews with parents of febrile infants 60 days or younger to generate potential items for the measure; (2) expert review with pediatric emergency medicine physicians and member checking with parents, who rated each item's clarity and relevance using 4-point scales; and (3) cognitive interviews with a new sample of parents, who gave feedback and rated the measure's ease of use on a 4-point scale. The measure was iteratively revised during each part of the development process. Results: In part 1, we interviewed 24 parents of 21 infants. Interviews revealed several themes: parents' experiences with medical care, communication, and decision making; parents' emotions, particularly worry, fear, and stress; the infant's outcomes valued by parents; and the impact of the infant's illness on the family. From these themes, we identified 22 potential items for inclusion in the measure. In part 2, 10 items were revised for clarity based on feedback from physicians and parents, primarily under the domains of parents' emotions and the infant's outcomes. In part 3, we further revised the measure for clarity and added an item. The final measure included 23 items and was rated as excellent in its ease of use. Conclusions: The 23-item parent-reported outcome measure includes the experiences and outcomes important to parents. Further studies are needed to evaluate the measure's psychometric properties.