Porto Santo Stefano is a seaport town on the west coast of Italy, in the municipality of Monte Argentario, in the Province of Grosseto, Tuscany. It is the municipal seat of Monte Argentario and one of the two major towns that form the township, along with Porto Ercole. The region is on the slopes of Mount Argentario, which dominates the whole area. Porto Santo Stefano is 150 kilometres northwest of Rome.