A vehicle rear portion structure that comprises: a first glass that is provided at a vehicle rear portion, and at which is formed a sunken portion that is sunken-in further toward a substantially vehicle lower side than portions adjacent thereto in a vehicle transverse direction; a connecting portion that is provided between the first glass and a second glass, and that leads drainage water, which flows from the sunken portion, to the second glass; and an additional member having a guide portion that extends toward a vehicle rear side from an upper portion of the second glass, and that guides the drainage water from the connecting portion to a position that is away, toward a vehicle rear side, from a vehicle rear side surface of the second glass.