A system for adjusting the height of a built-in household appliance, in particular a washing machine, includes a relay bar (1) extending from the front side of the machine to a rear corner (2) where an adjustable foot (3) is located, the rear end of said bar (1) being rotationally restrained in a horizontal gear (4) enmeshed with an adjacent vertical gear (5) housed in a casing (6) integral with the machine, said vertical gear (5) being aligned with a hole (2a) through which a seat (8) is secured on the machine. The foot (3) is formed by a base (3a) of non-skid material integral with a stud comprising a bottom shaped portion (3b) and a top threaded portion (3c), the seat (8) has a shape corresponding to the shape of the stud bottom portion (3b) that is rotationally restrained therein, and the vertical gear (5) has an internal thread, formed by means of a nut (9) locked in a corresponding seat (5a), in which the stud top portion (3c) is screwed. In this way it is possible to make the foot (3) with the stud integral with the non-skid base (3a), given that both of them remain still during the height adjustment, and dispensing with the play between the stud and the base (3a) makes the foot (3) more resistant to vibrations whereby the oscillations in the spin-drying phase are dramatically reduced.