Abstract: A longitudinally and angularly adjustable back rest assembly capable of being removably mounted on a motorcycle that has a rearwardly disposed frame portion that supports a second U-shaped frame that is secured to the base portion of an elongate seat. The seat is of sufficient length to support a single rider or a rider and a passenger. The back rest assembly may occupy any one of a number of longitudinal positions relative to the seat, and may be angularly adjusted when in any one of these positions. The back rest may accordingly be adjusted for use by either a single rider when he straddles the seat or a passenger when he occupies a like position rearwardly of the rider.