Objective: To synthesise international findings on the alcohol-dementia relationship and provide a cross-national comparison of the alcohol-dementia relationship with critical evidence for the relationship between alcohol use and dementia in under-studied populations. Design and setting: Individual participant data meta-analysis of 15 prospective epidemiological cohort studies from countries situated in five continents. Cox regression investigated the dementia risk associated with alcohol use. Sensitivity analyses compared lifetime abstainers with former drinkers, adjusted extensively for demographic and clinical characteristics, and assessed the competing risk of death. Participants: 24,472 community-dwelling individuals without a history of dementia at baseline and at least one follow-up dementia assessment. Main outcome measure: All-cause dementia as determined by clinical interview. Results: During 151,574 person-years of follow-up, there were 2,137 incident cases of dementia (14.1 per 1,000 person-years). In the combined sample, when compared with occasional drinkers (<1.3g/day), the risk for dementia was higher for current abstainers (HR: 1.29; 95% CI: 1.13, 1.48) and lower for moderate drinkers (25g/day-44.9g/day; HR: 0.79; 95% CI: 0.64, 0.98). When the combined sample was stratified by sex and gross domestic product, current abstainers had a greater risk of incident dementia when compared with light-to-moderate drinkers in both sexes and in the higher income countries. When comparing lifetime abstainers and former drinkers there were no consistent differences in dementia risk. Among current drinkers, there was no consistent evidence to suggest that the amount of alcohol consumed in later life was significantly associated with dementia risk. Adjusting for additional demographic and clinical covariates, and accounting for competing risk of death, did not substantially affect results. When analysed at the cohort level, there was considerable heterogeneity in the alcohol-dementia relationship. Conclusions: In a large and diverse international sample of older adults, the current study found that abstinence from alcohol is associated with an increased risk for all-cause dementia. Among current drinkers, there was no consistent evidence to suggest that the amount of alcohol consumed in later life was significantly associated with dementia risk.