Sliding screening device, comprising: an upper guide engageable along an upper side of a window; a lower guide engageable along a lower side of the window; a screening assembly comprising an upright, a movable bar parallel to the upright and a screening sheet having mutually opposite end edges, respectively engaged to the movable bar and to the upright; at least a first and a second slider each carried by one of the opposite ends of the movable bar and slidably engaged respectively along the upper guide and the lower guide, to guide the movement of the movable bar moving away and approaching the upright; stabilizing devices for maintaining the movable bar according to an orientation parallel to the upright; wherein said stabilizing devices comprise: at least one toothed pinion rotatably engaged to the first slider according to a rotation axis parallel to the longitudinal extension of the movable bar; a rack toothing operably engageable with the teeth of the at least one toothed pinion and extending along a side wall of the upper guide parallel to the direction of movement of the movable bar, further comprising at least one auxiliary toothed pinion, and an auxiliary rack toothing operably engageable with the teeth of at least one auxiliary toothed pinion and extending along the lower guide parallel to the direction of movement of the movable bar, characterized in that said at least one auxiliary toothed pinion is engaged to the second slider rotatably according to a respective axis of rotation perpendicular to the longitudinal extension of the movable bar, and in that said sliding screening device further comprises anchoring members (28, 29) for fixing at least the upright with respect to a vertical side of the window, wherein said anchoring members (28, 29) comprise a lower anchor operating between one end of the lower guide and a lower end of the upright, wherein the lower anchor comprises a toothed insert carried by the lower end of the upright and operatively engaged with the auxiliary rack toothing. an upper guide engageable along an upper side of a window; a lower guide engageable along a lower side of the window; a screening assembly comprising an upright, a movable bar parallel to the upright and a screening sheet having mutually opposite end edges, respectively engaged to the movable bar and to the upright; at least a first and a second slider each carried by one of the opposite ends of the movable bar and slidably engaged respectively along the upper guide and the lower guide, to guide the movement of the movable bar moving away and approaching the upright; stabilizing devices for maintaining the movable bar according to an orientation parallel to the upright; wherein said stabilizing devices comprise: at least one toothed pinion rotatably engaged to the first slider according to a rotation axis parallel to the longitudinal extension of the movable bar; a rack toothing operably engageable with the teeth of the at least one toothed pinion and extending along a side wall of the upper guide parallel to the direction of movement of the movable bar, further comprising at least one auxiliary toothed pinion, and an auxiliary rack toothing operably engageable with the teeth of at least one auxiliary toothed pinion and extending along the lower guide parallel to the direction of movement of the movable bar, characterized in that said at least one auxiliary toothed pinion is engaged to the second slider rotatably according to a respective axis of rotation perpendicular to the longitudinal extension of the movable bar, and in that said sliding screening device further comprises anchoring members (28, 29) for fixing at least the upright with respect to a vertical side of the window, wherein said anchoring members (28, 29) comprise a lower anchor operating between one end of the lower guide and a lower end of the upright, wherein the lower anchor comprises a toothed insert carried by the lower end of the upright and operatively engaged with the auxiliary rack toothing. at least one toothed pinion rotatably engaged to the first slider according to a rotation axis parallel to the longitudinal extension of the movable bar; a rack toothing operably engageable with the teeth of the at least one toothed pinion and extending along a side wall of the upper guide parallel to the direction of movement of the movable bar, further comprising at least one auxiliary toothed pinion, and an auxiliary rack toothing operably engageable with the teeth of at least one auxiliary toothed pinion and extending along the lower guide parallel to the direction of movement of the movable bar, characterized in that said at least one auxiliary toothed pinion is engaged to the second slider rotatably according to a respective axis of rotation perpendicular to the longitudinal extension of the movable bar, and in that said sliding screening device further comprises anchoring members (28, 29) for fixing at least the upright with respect to a vertical side of the window, wherein said anchoring members (28, 29) comprise a lower anchor operating between one end of the lower guide and a lower end of the upright, wherein the lower anchor comprises a toothed insert carried by the lower end of the upright and operatively engaged with the auxiliary rack toothing.