OBJECTIVE: The objective of this study was to develop a patient-reported outcome (PRO) to assess reduced muscle strength in sarcopenia. DESIGN: Qualitative research study. SETTING: University of Arkansas for Medical Sciences. PARTICIPANTS: Subjects with sarcopenia. MEASUREMENTS: Adults aged 55 years and older with sarcopenia (n = 12) attended open-ended, concept elicitation interviews to characterize the functional effects of reduced muscle strength on their lives. The resulting qualitative data were analyzed using a qualitative analysis software program (Atlas.ti [Atlas.ti GmbH, Berlin, Germany]) and a common set of codes was developed to summarize the data. Subsequently, the initial PRO measure was drafted. Cognitive interviews were then conducted with additional sarcopenia subjects (n = 12) to refine the measure. RESULTS: Qualitative interviews identified key concepts (eg, impacts) in the areas of activities of daily living, emotions, social activities, energy, balance, coordination, sleep, and strength. Based on data from the cognitive debriefing interviews (eg, understandability, relevance, suggestions to reword items), the PRO measure development team came to consensus on which items or parts of the instructions to retain, revise, or delete. The final measure included 14 items. CONCLUSION: The final PRO measure, the Age-Related Muscle Loss Questionnaire, can be used in both clinical practice and clinical trial settings to assess functional impacts of reduced muscle strength in sarcopenia.