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Advanced age is the most important risk factor for dementia and indeed many other neurological conditions. Measures of biological ageing such as DNA methylation age (DNAmAge) can give more information about the accumulation of age-related molecular damage than chronological age alone.Using post-mortem brain tissue from Swedish Twin Registry participants (n=49), we explored the relationship between lifestyle factors, dementia and DNAmAge measures from prefrontal cortex, cerebellum and blood.We observed that smoking was associated with a higher adjusted DNAmAge (PCBrainAge +6.4 years in prefrontal cortex, CI [2.5, 10.3], p=0.004). Conversely, a longer time spent in formal education was associated with a lower DNAmAge (DNAmClockCortical-4.8 years in prefrontal cortex, [-7.9, -1.8], p=0.007). We found no significant differences between DNAmAge of dementia cases vs controls, although amongst dementia cases there was a tendency towards higher DNAmClockCortical in prefrontal cortex for those with more advanced Braak stage on histopathological assessment (+ 3.4 years, [-0.68, 7.50], p=0.13). There were no clear associations between DNAmAge from brain and blood samples collected prior to death.In summary, these data highlight the impact of smoking and education on molecular biomarkers of brain ageing, and emphasise the role of these biomarkers in studying neurological disease.cem73@cam.ac.uk