External rearview mirror

External rearview mirror assembly for a vehicle including a mirror plate (1) connected by means of a position controlling actuator (11) to a support structure (20) which is accommodated within a housing (30) and mounted for articulation about a post (40) projecting from a base structure (60) mountable on the side of a vehicle. The support structure (20), which is constituted by a one-piece plastics part, includes fixing parts (22) for connection to the actuator (11) and the housing (30), a base plate (28) which closes an opening (32) in the base of the housing (30) and a sleeve (27) with a contoured lower surface which is urged against a complementarily contoured surface (52) disposed around a lower end of the post (40) by a spring (53). The base structure (60) is also constituted by a one-piece plastics part and includes the post (40), the contoured surface (52) formed on a protuberance (61) and plate (61) with a reinforcement structure comprising ribs (71) and receptor towers (72) formed on its rear surface.