There is a broad agreement that patient-reported outcome (PRO) assessment in health care should proceed from a strong conceptual basis, with rationales clearly articulated in advance concerning what is to be measured and how this is to be accomplished. The representation of the patient's perspective has been part of clinical trials for some time; but the formalization of, and broader emphasis on PROs has become increasingly important with the release of the draft guidance for industry on patient-reported outcomes. In response, we address the challenges in constructing the conceptual foundations for PRO assessment to support drug product labeling claims submitted to regulatory agencies worldwide.