The invention concerns a swivel joint ventilation flap comprising an air stream duct (10), a profiled body (18) the major part of which is at least arranged in the duct chamber, and a ring (26) co-operating with the duct and with the profiled member so that it supports the profiled body (18) in the duct while enabling the profiled body to be moved relative to the duct. Part at least of the inner surface of the chamber forms a spherical segment, the ring (26) has an outer surface forming a sphere portion of practically the same radius as the spherical segment, the ring (26) is arranged in the chamber at the outer surface of the profiled body (18). The profiled body (18) can slide relative to the ring (26). The ventilation flap is suitable for motor vehicle instrument panels.