Attenuated pestiviruses, in particular attenuated BVDV, wherein at least one mutation is in the coding sequence for glycoprotein Erns and at least another mutation in the coding sequence for Npro which preferably leads to combined inactivation of the RNase activity residing in glycoprotein Erns in addition to the inactivation of the (hypothesized) immunomodulating activity residing in Npro. Methods for attenuating pestiviruses such as BVDV, nucleic acids encoding the pestiviruses, in particular BVDV, compositions and vaccines comprising the attenuated pestiviruses, in particular BVDV, of the invention.