Objective: The aim of the current study was to examine the effect of negative life events and widowhood on the incidence of dementia. Methods: Data were from four Swedish longitudinal cohort studies with a total of nearly 2,000 participants and 8-25 years of follow-up. Seven stressful events were examined for which data were available in all cohorts. Clinical dementia diagnoses were made through medical and psychological examinations. Cox proportional hazards models were used to estimate the association between life events and dementia, adjusting for lifestyle and cardiovascular risk factors. Results: The experience of one stressful life event was not associated with dementia incidence, but two or more negative life events at baseline predicted higher risk for dementia (pooled HR:2.00). This was most apparent for the incidence of vascular dementia (pooled HR: 3.60) but not for Alzheimer disease (pooled HR: 1.29). Moreover, persons who were widowed and had experienced one or more negative life events were found to have a threefold risk for dementia. Conclusion: Widowhood augments the effect of negative life events on dementia incidence and negative life events specifically increase the risk for vascular dementia.