Epidemiological data on the incidence of cerebrovascular diseases in our country are scarce. A representative population-based study with a large denominator is required. To present the design of the study on stroke incidence in Spain, entitled Iberictus. We conducted a prospective, population-based study on the incidence of strokes and transient ischemic attacks, in which it is possible to distinguish: 1) population with a steady risk, which was well defined and had a broad denominator. We included all the cases in which the first episode of acute cerebrovascular disease was diagnosed among those over the age of 17 years (with no upper age limit) with their habitual residence in the areas of study between the 1st January and 31st December 2006: Lugo, Segovia, Talavera de la Reina, Mallorca and Almeria (total denominator, 1,440,997 inhabitants; minimum denominator per area, 100,000 inhabitants); 2) source of multiple and complementary data: hospital records (minimum basic data set, discharge abstracts), emergency and primary care records for the area with diagnostic codes 430-39 and 674.0 (International Classification of Diseases-9), population-based mortality records; 3) standardised definitions: diagnostic categorisation (MONICA-World Health Organisation, 1987), pathological classification (ischaemia, haemorrhagic), topography and aetiology; 4) presentation of data in suitable age groups, by sex and overall; 5) pilot study and analysis of inter-observer agreement among researchers. With this design, the Iberictus study satisfies the methodological criteria as an 'ideal' study of the incidence of acute cerebrovascular diseases proposed by Malgrem, Sudlow and Warlow, and represents a unique opportunity to further our knowledge of the epidemiology of strokes in our country.