Fratiglioni L, Matthews FE, et al. Dementia in Western Europe: epidemiological evidence and implications for policy making. Lancet Neurol. 2016;15(1):116–124. 3. Virués-Ortega J, de Pedro-Cuesta J, Vega S, et al. Prevalence and European comparison of dementia in a ≥75-year-old composite population in Spain. Acta Neurol Scand. 2011;123(5):316–324. 4. Rodríguez-Sánchez E, Mora-Simón S, Patino-Alonso MC, et al. Prevalence of cognitive impairment in individuals aged over 65 in an urban area: DERIVA study. BMC Neurol. 2011;11(1):147. 5. Tola-Arribas MA, Yugueros MI, Garea MJ, et al. Prevalence of dementia and subtypes in Valladolid, northwestern Spain: the DEMINVALL study. PLoS One. 2013;8(10):e77688. 6. de Hoyos-Alonso MC, Bonis J, Tapias-Merino E, Castell MV, Otero A. Estimación de la prevalencia de demencia a partir del análisis de bases de datos sobre uso de fármacos. La situación en La Comunidad de Madrid (España). Neurología. 2016;31(1):1–8. 7. Perera G, Pedersen L, Ansel D. Dementia prevalence and incidence in a Federation of European electronic health record databases—the European medical informatics framework resource. Alzheimers Dement. 2018;14(2):130–139. 8. Drummond N, Birtwhistle R, Williamson T, Khan S, Garies S, Molnar F. Prevalence and management of dementia in primary care practices with electronic medical records: a report from the Canadian primary care sentinel surveillance network. CMAJ Open. 2016;4(2): E177–E184. 9. van Bussel EF, Richard E, Arts DL, et al. Dementia incidence trend over 1992-2014 in the Netherlands: analysis of primary care data. PLoS Med. 2017;14(3):e1002235. 10. Wilkinson T, Ly A, Schnier C. Identifying dementia cases with routinely collected health data: a systematic review. Alzheimers Dement. 2018;14(8):1038–1051. 11. Zunzunegui Pastor MV, Ser T del, Rodríguez Laso A, García Yébenes MJ, Domingo J, Otero Puime A. Demencia no detectada y utilización de los servicios sanitarios: implicaciones para la atención primaria TT - Non-detected dementia and use of the health services: implications for primary care. Aten Primaria. 2003;31(9):581–586. 12. Bolíbar B, Fina Avilés F, Morros R, et al. [SIDIAP database: electronic clinical records in primary care as a source of information for epidemiologic research]. Med Clin (Barc). 2012;138(14):617–621. Spanish 13. García-Gil MM, Hermosilla E, Prieto-Alhambra D, et al. Construction and validation of a scoring system for the selection of high-quality data in a Spanis EPIDEMIOLOGY AND RISK FACTORS OF DEMENTIA W M van der Flier, P Scheltens J Neurol Neurosurg Psychiatry 2005;76(Suppl V):v2–v7. Dementia refers to a syndrome that is characterised by progressive deterioration of cognitive functions. Neuropsychiatric symptoms, such as apathy, agitation, and depression, are also common. With increasing loss of function, a patient is gradually robbed of his or her independence. Eventually, placement in a nursing home may be necessary. Patients with dementia usually survive 7—10 years after onset of symptoms. Dementia places a tremendous burden not only on caregivers, but also on society, and has already been established as one of the major challenges of this century.1 Epidemiology refers to the medical science that studies frequencies of disease.2 Measures of frequency that are often used in epidemiology are prevalence and incidence. The concept of prevalence refers to the number of patients with a disease at a certain moment in time, whereas measures of incidence reflect the number of new cases over time. Although important for health care planners, the knowledge of frequency of disease in itself is not the goal of epidemiology. Rather, the aim is to gain insight into the mechanisms that cause disease, eventually to be able to cure or prevent disease. Therefore, frequencies are studied in relation to determinants, or risk factors. Although marked as ‘‘the epidemic of our century’’, still surprisingly little is known about the epidemiology of dementia. In this chapter, a brief overview will be given of the epidemiology and risk factors of dementia. Furthermore, we comment on some specific methodological