Itsasondo is a town and municipality in the Goierri region of the province of Gipuzkoa, in the autonomous community of the Basque Country in northern Spain.
It is one of the municipalities that make up the Goierri, an inland district of Gipuzkoa in the Basque Country. The town is known by the name Itsasondo in Basque, which is the form used officially.