The invention relates to a backrest unit for a motor vehicle seat, in particular a rear seat comprising a backrest and support connected thereto. A guide rail is arranges on the rear surface of the backrest on an x-z plane. A slide is movably mounted on the guide rail and is lockable therein in different positions. When a control device associated with the slide is actuated, it brings the slide from a normally locking position into a released position. A support comprises a near end which is hinged on the slide and a distant end which is fixable to a bodywork part.