The study presents a 3D lithospheric density model of the Scandinavian mountain chain (Scandes) and adjacent areas of the Fennoscandian shield. The high topography of the Scandes correlates with a Bouguer gravity low, indicating isostatic compensation. Seismic results, however, do not image a crustal root below the Scandes. Taking into account the geometry of the base lithosphere, isostatic balance can be achieved by introducing a high-density lower crust below the Fennoscandian shield with a thickness up to 25 km. This structure tapers out below the Scandes. A second feature necessary to explain the gravity field and to balance isostatically the model is the Trans-Scandinavian Igneous Belt (TIB). The TIB is partly adjacent to and partly coincident with the Scandes. The resulting isostatic balanced model explains the gravity field of the Fennoscandian shield except for two areas: the northern and southern Scandes, which coincide with Cenozoic uplift centres. Thus, a low-density domain may be found at shallow depth below the Moho.