BACKGROUND: Adherence to the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet, which combines higher consumption of vegetables, berries, nuts, whole grains, olive oil, fish, beans and poultry, with lower consumption of meat, sugars and saturated fats, is a promising strategy to prevent dementia. However, evidence in populations with non-US food culture, especially from Europe, is limited. OBJECTIVES: To evaluate the association of a French-adapted MIND diet score with gray matter volumes, white matter microstructure and incident dementia. DESIGN AND SETTING: This longitudinal study included participants from the population-based Three-City Bordeaux cohort (≥65 years), with a follow-up from June 2001 to February 2018. PARTICIPANTS: Dementia-free participants at dietary assessment, in 2001-2002, who underwent systematic detection of incident dementia (over up to 7 visits). A subset of the cohort was included in an ancillary MRI study in 2010-2011. MEASUREMENTS: A French-adapted MIND diet score (range, 0-15) was computed from a 148-item Food Frequency Questionnaire and a 24-hour recall administered at home. Incident dementia and its subtypes were adjudicated by an expert committee; and gray matter volumes and white matter microstructure were assessed by 3D-T1 MRI and diffusion-MRI. RESULTS: Among 1,412 participants (mean age, 75.8 [SD, 4.8]; 63% women), followed for a median of 9.7 years (maximum 16.3 years), 356 (25.2%) developed incident dementia. In multivariable-adjusted Cox model, a higher French MIND diet score was associated with lower risks of dementia and AD (hazard ratios for 1-point of score = 0.89 [95% confidence interval, 0.83-0.95] and 0.88 [0.81-0.96], respectively). In Tract-Based Spatial Statistics analysis of 175 participants included in the MRI sub-study, a higher MIND diet score was associated with lower diffusivity values in the splenium of the corpus callosum (P < .05 after Family-Wise Error-correction). In contrast, there was no significant association of the adapted MIND diet score with gray matter volumes in Voxel-Based Morphometry analysis. CONCLUSION: In this cohort of French older adults, higher adherence to the French MIND diet was associated with a lower dementia risk and with preserved white matter microstructure. These results provide further evidence for a role of the MIND diet in the prevention of dementia.