The population of San Sebastian grew in a progressive way along the 20th century. Between(among) 1900 and 1930 the growth was regular, happening to double in them only 35 years that they separate 1930 of 1965. This recovery in the demographic growth met attenuated by a minor growth from the decade of the 70s, managing to diminish the population for the first time in the century at the end of the 80s, as consequence of the widespread fall of the birthrate in the whole country.

The current growth of the population is slow, though the phenomenon of the immigration, still incipient in the city (the immigrants, 2006, come to 5 % of the registered ones, according to the Society of Promotion of the Town hall of San Sebastian), can affect in a recovery of the demographic growth. According to the last information, on January 1, 2005, the total population places in 182.930 inhabitants, of which 96.822 are women (53 %) and 86.108 men (47 %).