Background: The validated Investigator Global Assessment for Atopic Dermatitis (vIGA-AD™) is a standardized severity assessment for use in clinical trials and registries for atopic dermatitis (AD). Objectives: To investigate the reliability, validity, responsiveness and within-patient meaningful change of the vIGA-AD. Methods: Data were analysed from adult patients with moderate-to-severe AD in the BREEZE-AD1 (N = 624 patients; NCT03334396), BREEZE-AD2 (N = 615; NCT03334422) and BREEZE-AD5 (N = 440; NCT03435081) phase III baricitinib clinical studies. Results: Across studies, test–retest reliability for stable patients showed moderate-to-good agreement [range of Kappa values for Patient Global Impression of Severity–Atopic Dermatitis (PGI-S-AD), 0·516–0·639; for Eczema Area and Severity Index (EASI), 0·658–0·778]. Moderate-to-large correlations between vIGA-AD and EASI or body surface area (range at baseline, 0·497–0·736; Week 16, 0·716–0·893) supported convergent validity. Known-groups validity was demonstrated vs. EASI and PGI-S-AD (vIGA-AD for severe vs. moderate EASI categories at baseline, P < 0·001). Responsiveness was demonstrated vs. EASI (P < 0·001 for much improved vs. improved and improved vs. stable). Anchor- and distribution-based methods supported a vIGA-AD change of –1·0 as clinically meaningful. These findings are limited to populations defined by the studies’ inclusion and exclusion criteria. Conclusions: The vIGA-AD demonstrated sufficient reliability, validity, responsiveness and interpretation standards for use in clinical trials. What is already known about this topic? A description of the development of the validated Investigator Global Assessment for Atopic Dermatitis (vIGA-AD™) has been published previously. What does this study add? The current study validates the vIGA-AD by demonstrating appropriate test–retest reliability, convergent validity, known-groups validity and responsiveness across three baricitinib clinical studies. In addition, a 1-point change was identified as a clinically meaningful patient-perceived change minimal clinically important difference in the vIGA-AD. What are the clinical implications of the work? The vIGA-AD is a measure for investigator assessment of atopic dermatitis suitable for use in clinical research.