Portugalete is a town lying to the west of Bilbao in the province of Biscay in the Autonomous Community of Basque Country, northern Spain. The town has 45,766 inhabitants and is part of Bilbao's metropolitan area. It is located at the mouth of the Estuary of Bilbao, on the left bank. Its land area is only 3.21 km², resulting in a population density of 15,908.4 persons/km², the fifth-most densely populated municipality in Spain.