This paper describes the design and performance of a modular wideband high-voltage dc (HVDC) reference divider with a ratio uncertainty of less than 0.005% at 1000 kV. The divider has a maximum nominal voltage of 1000 kV when five 200-kV modules are stacked on top of each other. The divider is used for traceable calibration of HVDC measuring systems in customers' laboratories. The first priority in the design was the accuracy of HVDC measurements. In addition, the divider was designed to have wide bandwidth, both to enable measurement of ripple voltages and to prevent damage during possible flashovers.