The invention relates to a method for the dewatering of sludge on a screen, wherein a flocculant is admixed with sludge, whereafter the sludge is at least partially dewatered, the flow behaviour of the sludge on the screen being optically detected and the amount of flocculant to be admixed being set according to the free screen surface in a control region. The invention is primarily characterized in that the control region is arranged at a point of the cleaned screen in the inlet area of the sludge, for example at the edge. The invention also relates to a device for the dewatering of sludge, comprising a flocculant feed device and a screen downstream of the flocculant feed device, wherein a device, in particular a camera, is provided for optically detecting the flow behaviour of the sludge and is connected via a control system to the flocculant feed device for regulating the amount of flocculant, said device being characterized in that the device (11), in particular the camera, is designed such that it detects a control region in the inlet area (10) of the cleaned screen. In this way, regulation can be achieved for an optimal feed amount of flocculant in a straightforward manner regardless of the material feed and the sludge type.