BACKGROUND Approximately 50 000 adults in the United States are diagnosed with GH deficiency, which has negative impacts on cognitive functioning, psychological well-being, and quality of life. OBJECTIVE This paper presents development and validation of a patient-reported outcome measure (PRO), the Treatment-Related Impact Measure-Adult Growth Hormone Deficiency (TRIM-AGHD). The TRIM-AGHD was developed to measure the impact of GH deficiency and its treatment. METHODS The development and validation of the TRIM-AGHD was conducted according to the Food and Drug Administration guidance on the development of PROs. Concept elicitation, conducted in three countries included interviews with patients, clinical experts, and literature review. Qualitative data were analyzed based on grounded theory principles, and draft items were cognitively debriefed. The measure underwent psychometric validation in a US clinic-based population. An a priori statistical analysis plan included assessment of the measurement model, reliability, and validity. Item functioning was reviewed using item response theory analyses. METHODS Forty-eight patients and six clinical experts participated in concept elicitation and 169 patients completed the validation study. METHODS TRIM-AGHD was measured. RESULTS Factor analysis resulted in four domains: energy level, physical health, emotional health, and cognitive ability. The item response theory confirmed adequate item fit and placement within their domain. Internal consistency ranged from 0.82 to 0.95 and test-retest ranged from 0.80 to 0.92. All prespecified hypotheses for convergent validity and all but two for discriminant validity were met. CONCLUSIONS The final 26-item TRIM-AGHD can be considered a reliable and valid PRO of the impact of disease and treatment for adult GH deficiency.