An arm rest assembly for a motorcycle passenger seat includes a vertically adjustable mount secured to the typical backrest behind the passenger seat. A U-shaped tubular member includes a medial portion rotatably secured in the mount, and arm rest cushions secured to opposed side arm portions. The U-shaped member is rotatable through an arc of approximately 180° about the axis of the medial portion, the range being limited by stop members joined to the medial portion. The side arm portions extend rearwardly to support baggage, or rotated to an upwardly extending disposition in which the passenger may mount or dismount the passenger seat, to a forwardly extending disposition in which the side arm portions extend to support the arms of the passenger and to provide side support for the passenger.