BACKGROUND This study's purpose was to assess the minimal important difference (MID) for the Treatment-Related Impact Measure-Adult Growth Hormone Deficiency (TRIM-AGHD), a patient-reported outcome measure assessing growth hormone deficiency (GHD) impacts. The measure was demonstrated to have adequate psychometric measurement properties, and be reliable and valid. For scores to be interpretable, the TRIM-AGHD must be responsive to treatment benefit and the MID in scores quantified. METHODS A prospective, non-interventional, observational, clinic-based survey study of naïve-to-treatment adult GHD patients (N = 98) was conducted. Key assessments were at baseline and follow-up (between 4 and approximately 8 weeks), with weekly telephone monitoring post-baseline (last n = 34 patients). Responsiveness was evaluated using the effect size of change scores from baseline to follow-up. MID estimates were derived from distribution-based (half standard deviation [0.5 SD], standard error of measurement [SEm]) and anchor-based methods (patient global rating of change [PGRC]) using change scores from baseline to initial report of minimal improvement in GHD severity. Findings from each method were converged to establish an acceptable MID. RESULTS Patients were mean age 49.7 years, 65.6% female, and 76.0% Caucasian. The TRIM-AGHD was highly responsive to treatment with the total score effect size being 1.38. For the total score, the 0.5 SD was 8.09 and the SEm was 2.66. The difference found using the PGRC was 20.43. The converged MID value for the total score was 10 points. CONCLUSIONS The TRIM-AGHD is a highly responsive measure assessing AGHD treatment impacts. A 10-point change score is considered a clinically meaningful improvement.