Abstract: The adjustable support assembly is for supporting a component of a piece of furniture, such as a backrest or armrest of a sofa. The component is fixed to the upper end of a shaft. The lower end of the shaft is insertable into an elongated hollow member, fixed to the frame of the sofa with a mounting bracket connected to the hollow member and screwed to the frame. A locking device releasably holds the shaft in any one of a plurality of angular positions with respect to the hollow member when the shaft is substantially engaged in the hollow member. The orientation of the component may therefor be easily adjusted and locked when a person sitting on the sofa so desires.