A chair, includes a seat structure and a backrest structure arranged pivotally to the seat structure. An armrest is arranged pivotally to the backrest structure through a pivotal connection, and a link mechanism is journalled to the structures of the seat and the backrest, respectively, the link mechanism actuating and controlling the armrest to maintain its pivotal orientation in any pivotal position of the backrest relative to the seat. The armrest is adjustable in the length direction of the backrest through the pivotal connection which is arranged displaceable on the backrest structure, and the pivotal orientation of the armrest is controlled via a sliding engagement between a lever arm, adjoining the armrest at an angle thereto, and an actuator link included in the link mechanism and displaceable thereby with respect to the backrest so as to extend substantially in the length direction of the backrest in all its positions of displacement.