An adjustable chair is described comprising a body supported by a base and having a frame constituted by two parts and hingedly connected together.The main characteristic of the present invention lies in the fact that it includes a mechanism having a first body hinged about a pin rigidly connected to the base and having its front end rigidly connected to the part associated with the seat, and a second body and having a rear end fixed to the part associated with the seat back and a front end connected, by spring means, to a central portion of the said first body.