Abstract: A motor vehicle seat assembly including a base portion affixed to the motor vehicle, a seat portion movably attached to the base portion, and a seat adjustment mechanism operatively interposed between the seat portion and the base portion for enabling selective adjustable movement of the seat portion relative to the base portion. In order to enable a passenger's safety belt to be attached at the movable seat portion, a locking pin mechanism is provided which may be selectively activated to lock the seat portion relative to the base portion thereby to prevent relative movement therebetween. The seat adjustment mechanism may be formed with a longitudinal seat adjustment device which enables forward and rearward movement of the seat portion and with tilt adjusting devices enabling height adjustment of the seat. The locking pin mechanism may be arranged to lock at least one or both of the longitudinal seat adjustment mechanism and the tilt adjustment devices.