The invention relates to an extracorporeal blood treatment device having a hydraulic system II which comprises several flow paths, wherein the blood treatment device has a control unit (40) which provides an operating mode for a disinfection of the hydraulic system with a liquid that can be supplied via one of the flow paths. The invention further relates to a method for operating an extracorporeal blood treatment device with a hydraulic system comprising several flow paths. The blood treatment device according to the invention is characterized in that the hydraulic system II has a valve device (23) that provides several switching positions. The valve device (23) has an inlet (25A) for the liquid for the disinfection of the hydraulic system and several outlets (26A, 27A, 28A), wherein in one 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 several outlets (26A, 27A, 28A). The inlet (25A) of the valve device (23) is fluidically connected to the flow path via which liquid can be delivered for the disinfection of the hydraulic system II, and the outlets (26A, 27A, 28A) of the valve device (23) are each fluidically connected to another flow path of the hydraulic system, such that liquid can be delivered simultaneously to the individual flow paths.
