The complete nucleotide sequence of isolates of Cucumber vein yellowing virus (CVYV) has been determined. The viral genome comprises 9734 nucleotides, excluding a 3'-terminal poly(A) sequence. The genome of CVYV has a 5'-non coding and a 3' non coding region of respectively 67 and 240 nucleotides. The RNA of CVYV encodes a single polyprotein of 3148 amino acid residues and has a deduced genome organization and motifs typical for a member of the family Potyviridae. However, CVYV is atypical because it lacks a coding sequence region for the putative helper-component as well as conserved helper-component-proteinase motifs which may account for its vector relations. All the present coding regions were compared to those from several members of the Potyviridae family. CVYV is most closely related to Sweetpotato mild mottle virus confirming its assignation to the genus Ipomovirus, despite similarities with tritimoviruses.