Background: Left ventricular hypertrophy (LVH) is most commonly an indicator of target organ damage due to hypertension and may serve as a marker for chronicity of blood pressure elevation and as an indicator of the long-term burden of vascular risk factors. We assessed whether LVH measured by 12-lead ECG was associated with incident dementia in the Atherosclerosis Risk in Communities – Neurocognitive Study (ARIC-NCS). Methods: Our analysis included 12,665 individuals (23% black race, 56% female, mean age 57) who attended visit 2 in 1990-92. Cornell voltage (SV3 + RaVL) was derived from 12-lead ECG at visit 2 (1990-92), visit 3 (1993-95) and visit 4 (1996-98) as a continuous variable, and the gender-specific Cornell voltage criteria (SV3 + RaVL > 28mm for men, and >22mm for women) was used to define LVH as a dichotomous variable. Incident dementia was defined using a validated algorithm consisting of a full neuropsychological assessment, interviews, informant interviews, hospital discharge codes, or diagnostic codes from death certificates. A cox proportional hazards model was used to evaluate the association between LVH and incident dementia. LVH and Cornell voltage were modeled as time-dependent variables and covariates were updated at each visit. Follow-up time was from baseline until date of dementia, end of follow-up, or the end of 2013, whichever came first. Results: During a mean follow-up of 18 years, we identified 544 participants with LVH and 1195 incident dementia cases. LVH was associated with a higher risk of dementia: multivariable hazard ratio (HR) 1.91, 95% confidence interval (CI) 1.48-2.46 (Table). A 1-standard deviation increase in Cornell voltage (5 mm) was associated with a higher risk of dementia, HR (95% CI) = 1.10 (1.04-1.17). Conclusion: In this large population-based study, LVH measured in mid-life was associated with an increased risk of dementia. Additional research should confirm this association, and these results underscore the need for hypertension control to prevent subclinical brain injury.