The purpose of CIPM comparison CCEM-K8 was to compare the scaling capabilities up to 1000 V dc of national metrology institutes. Fifteen institutes participated, with the Istituto Elettrotecnico Nazionale Galileo Ferraris (Turin, Italy) acting as pilot laboratory. Circulation of the travelling standard, a resistive voltage divider, started in October 1998 and ended in June 2001. The technical protocol requested the measurement of voltage ratios 1000 V/10 V and 100 V/10 V, the measurement of other ratios being optional. For the mandatory ratios, the measurement methods used by the participants are described and the evaluation of the key comparison reference value and the degrees of equivalence is reported in detail. For these ratios, the relative uncertainty of the comparison, given by the combination of the uncertainty of the reference value and the instability of the transfer standard, was about 0.23×10^-6 at 95% level of confidence. Results for the supplementary ratios are reported in an appendix. With certain exceptions, agreement between the results is satisfactory; in some cases the measurement uncertainty was underestimated.