Background: Dementia is typically known for its insidious onset and slowly progressive course, but a subgroup deteriorates fast and dies within years or even months. Objective: The purpose of this study was to characterize dementia patients with a rapidly progressive course to death and evaluate their cause of death. Methods: We retrospectively included all patients from the Amsterdam Dementia Cohort who died within two years after diagnosis. We evaluated the characteristics of these rapid progressors and compared them to patients known to be alive two years after diagnosis (‘non-rapid mortality’). Results: We included 129 dementia patients (13% of our total cohort with known follow-up) with rapid mortality (age 72±10 y [29% <65 y], 70[55%]M, MMSE 20±5). Mean(SD) survival was 12±7 months. Compared to non-rapid mortality patients (n = 892; age 68±9, 503(56%)M, MMSE 22±5), patients with rapid mortality were slightly older at time of diagnosis, had lower MMSE scores, more depressive symptoms and higher prevalence of a cardiovascular history (all p < 0.05). Alzheimer’s disease (AD, 43%) was most frequent in patients with rapid mortality, but the occurrence was much lower compared to non-rapid mortality patients (71%), while all other dementia diagnoses, especially Creutzfeldt-Jakob disease (CJD), vascular dementia (VaD), and frontotemporal dementia (FTD), were more frequent (p < 0.001). There were no specific characteristics for AD patients with rapid versus non-rapid mortality, especially APOE genotypes and CSF-profiles were comparable (p > 0.70). Cause of death was highly variable without a clear relation to dementia diagnosis, with exception of dementia itself in CJD, intracerebral hematoma in VaD, and motor neuron disease in FTD. Conclusions: Short survival is relatively common (∼13% in our cohort) and occurs in all different types of dementia, with overrepresentation of non-AD dementias like CJD, VaD, and FTD.