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A considerable number of studies have shown that Spain is one of the countries on the European continent with a high level of inbreeding and that, in general, this level decreased more quickly and later than the levels in the rest of Europe. The types and frequencies of consanguineous marriages (up to third cousins), the mean inbreeding coefficient, and secular trends have been studied within the Basque Country (Alava Province) using information from ecclesiastic dispensations from 1831 to 1980. A total of 5583 consanguineous marriages were registered in Alava over the whole period (150 years), and 79 different categories of relationship were observed. The analysis of the structure of consanguinity has shown some appreciable levels of close consanguineous unions: 0.08% (uncleniece or aunt-nephew marriages) and 0.96% (first-cousin marriages) of the total number of marriages. This seems to be a common phenomenon among provinces of northern Spain. The rates of total consanguinity and the mean coefficient of inbreeding in the population of Alava from 1861 to 1980 were 4.62% and 0.00124, respectively. The temporal trend pattern of inbreeding in Alava closely fits the pattern observed in other large European populations: France, Italy, and Belgium. This early fall in the level of inbreeding in Alava compared to the levels found in both large and small populations in central and western Spain might be due to the early industrial development of the Basque Country and the resulting loss of importance of landownership.