Mild Behavioral Impairment (MBI) reflects later-life emergence of persistent neuropsychiatric symptoms and is increasingly recognized as an early manifestation of neurodegenerative disease, yet cerebellar correlates remain underexplored. We tested whether cerebellar morphometry is associated with incident MBI in mild cognitive impairment (MCI).

Using longitudinal Alzheimer’s Disease Neuroimaging Initiative data, MBI was derived from Neuropsychiatric Inventory/ Neuropsychiatric Inventory-Questionnaire items mapped to five diagnostic domains and defined as new symptoms persisting for ≥2 consecutive visits after a symptom-free baseline. Of 530 MCI participants without baseline symptoms, 181 who developed MBI were matched 1:1 to controls by age, sex, and education. DeepCERES quantified lobular cerebellar cortical thickness and asymmetry from 3T T1-weighted MRI. We used logistic regression with false discovery rate correction and conducted domain-specific analyses (affective dysregulation, impulse dyscontrol, decreased motivation).

MBI cases had lower Mini Mental State Examination scores and higher dementia conversion than controls. Greater thickness in right cerebellar lobules IV (OR 1.215), V (OR 1.122), and VIIIB (OR 1.169), and greater asymmetry in right lobule V (OR 1.035), were associated with incident MBI. Affective dysregulation showed the strongest, largely right-lateralized associations and greater interhemispheric asymmetry. Main results were unchanged after separate sensitivity adjustments for Mini Mental State Examination scores and for index-visit psychiatric medication use.

Incident MBI in MCI is linked to right-lateralized cerebellar cortical thickening and asymmetry, most prominently for affective dysregulation. These patterns may reflect early compensatory and/or neuroinflammatory processes within cerebello–cortical circuits relevant to affect regulation.