OBJECTIVES: The Treatment Related Impact Measure for Adults with Growth Hormone Deficiency (TRIM-AGHD), a patient reported outcome (PRO) measure assessing the impact of growth hormone deficiency (GHD) in adults was developed in accordance with the FDA guidance on PRO measure development. Prior validation work determined that the TRIM-AGHD had adequate measurement properties, and was reliable and valid. However, for TRIM-AGHD scores to be interpretable, it is critical that the TRIM-AGHD be responsive to treatment benefit and the minimally clinical important difference in scores (MCID) quantified. METHODS: A clinic based study, recruiting naïve-to-treatment adult GHD patients, was conducted. Assessments were at baseline visit (treatment start), weekly by telephone, and 8 week follow-up visit. Responsiveness was evaluated using the effect size of change scores from baseline to follow-up. The MCID estimates were derived from distribution-based [½ standard deviation (½SD), standard error of measurement (SEM)] and anchor-based methods [using the patient global rating of change (PGRC)] using change scores from baseline to initial report of minimal improvement in their GHD severity. Results were then triangulated to suggest an acceptable MCID. RESULTS: Ninety-six patients completed the study, mean age 49.65 years (range 29–68), 65.62% female, 76.04% white, and the primary cause of GHD was head trauma (17.71%) [unknown cause 46.88%]. At follow-up, the TRIM-AGHD was shown to be highly responsive to treatment with the total score effect size being 1.38 (subdomains ranging between 1.22 and 1.36). For the total score, the ½SD was 8.09, the SEM was 2.66, and the anchor-based (PGRC) was 20.43. The suggested MCID based on averaging these methods is 10.40. CONCLUSIONS: The TRIM-AGHD is a highly responsive measure of the impact of adult growth hormone treatment. A change score of 10.40 points on the measure can be considered a clinically meaningful improvement in patient functioning and well-being.