Abstract: An armrest (1) for a chair (S) including an upright element (2) substantially vertical provided in the lower part (2a) with fixing means (3) to a seat (L) of said chair (S) and supporting in the higher part (2b) an armrest element (4). The upright element (2) and the armrest element (4) are coupled through sliding means (5) suitable to allow the movement of the armrest element (4) in order to vary the distance of the front end (4a) of said armrest element (4) as regards the front end (A) of the seat (L).