Researchers examined whether DunedinPACNI, an MRI-derived measure of brain aging, was associated with blood-based indicators of biological aging in 746 adults across two independent midlife cohorts. Faster DunedinPACNI was associated with higher levels of multisystem biological aging in both cohorts and greater changes in aging-related blood biomarkers over 7–15 years in a longitudinal subgroup of 224 participants.