An air-guiding system for a ventilation system of a vehicle comprises a supply duct (12), three discharge ducts (14, 16, 18) branching off from the latter and a control part (20), which has a main guiding element (24) with a main guiding vane (24a) and also a secondary guiding element, kept at a distance from the latter, with a secondary guiding vane (26) and can be pivoted about a pivot axis (22). The main guiding element (24) is provided with an auxiliary guiding vane (24b) which is connected at one of its ends to the main guiding vane (24a) at a fixed angle and on the opposite side has a free end, the main guiding vane (24a) together with the secondary guiding vane (26) distributing, as a function of the pivoting position of the control part (20), an air flow, arriving from the supply duct (12), between the discharge ducts (14, 16, 18), and the auxiliary guiding vane (24b) blocking off or at least constricting a direct flow path between two adjacent outflow ducts (16, 18). With just one control part (20) the air flow can be distributed from the supply duct (12) to three outflow ducts (14, 16, 18) in a manner favorable for flow and optimally.