A motor-vehicle door comprises a structure including an inner frame (3), a carrier (5) fixed to the inner frame (3), for supporting a plurality of auxiliary members of the door, and a trimming panel (6, 7) which covers the carrier (5) and the inner frame (3) on the inner side of the door. The carrier (5) is made of fibre-reinforced synthetic material and it is rigidly connected to the inner frame (3) and it is configured to also serve as a structural reinforcement for said inner frame. The carrier (5) also has at least one portion (50, 52) exposed to view, not covered by said trimming panel (6, 7) and having a structure and a configuration such to directly serve the function of trimming panel at the exposed portions thereof. In a variant, the frame is constituted by a quadrangular framework constituted by one or more C-section elements defining an upper crosspiece, a lower crosspiece and two uprights which connect the ends of said crosspieces to each other. An outer panel (4) having a structure (40) configured to absorb impact energy, in particular a honeycomb-like structure, is provided for in this case.