The invention relates to an extracorporeal blood treatment device comprising a hydraulic system II comprising a plurality of flow paths, the blood treatment device having a control unit 40 which provides an operating mode for disinfecting the hydraulic system with a liquid which can be supplied via one of the flow paths. Moreover, the invention relates to a method for operating an extracorporeal blood treatment device with a hydraulic system comprising a plurality of flow paths. The blood treatment device according to the invention is characterized in that the hydraulic system II has a valve device 23 which provides several switching positions. The valve device 23 has an inlet 25A for the liquid for disinfecting the hydraulic system and a plurality of outlets 26A, 27A, 28A, wherein in a switching position the inlet 25A is connected to one of the outlets 26A, 27A, 28A and in another switching position the inlet is connected to a plurality of outlets 26A, 27A, 28A. The inlet 25A of the valve device 23 is in fluid communication with the flow path via which liquid for disinfecting the hydraulic system II can be supplied, and the outlets 26A, 27A, 28A of the valve device 23 are in fluid communication with another flow path of the hydraulic system, so that liquid can simultaneously be supplied to the individual flow paths.