Abstract: A back rest for the seats of motor vehicles has a frame which carries a relatively short adjustable shoulder support. The sides of the shoulder rest are mounted on pairs of links, and the shoulder rest can be pivoted by two levers each of which is pivotable relative to the frame jointly with one of the links at the respective side of the shoulder rest and is attached to the shoulder rest by a pin-and-slot connection. The levers can be pivoted by reciprocable slides which are mounted on the frame and have followers extending into cam slots of the corresponding levers. The slides can be moved up and down longitudinally of the respective sides of the frame by rack and pinion drives which can be operated by a hand wheel or by a motor. The links cooperate with the levers to impart to the shoulder rest a composite movement including a translatory movement which is superimposed upon a pivotal movement about an imaginary axis located below and remote from the lowermost portion of the shoulder rest.