In a 1990 outbreak, a virus isolated in Taiwan from the intestines of ducks showing signs of hepatitis was tentatively classified as a picornavirus on the basis of physical, chemical, and morphological characteristics. The virus was cloned and then found not to be type 1 duck hepatitis virus (DHV-1) or a new serotype of duck hepatitis virus (N-DHV) by serum neutralization. Complete genome sequencing indicated that the virus genome had 8351 nucleotides and the typical picornavirus genome organization (i.e., 5' untranslated region (UTR)-L-P1 (VP 4-2-3-1)-P2 (2A-B-C)-P3 (3A-B-C-D)-3' UTR-poly A). One open reading frame encoded 2521 amino acids, which makes this virus one of the largest picornaviruses, second only to equine rhinitis B virus of the genus Erbovirus. Its L protein was the largest within the family Picornaviridae (451 amino acids) and suspected to be a trypsin-like protease. The 235-nucleotide 3' UTR region was of intermediate size, quite long compared to other picornaviruses but shorter than other picornaviruses of duck-origin (DHV-1 and N-DHV) and had four regions of secondary structure. The 2A protein was composed of only 12 amino acids, which is the shortest of any member of the family Picornaviridae. Phylogenetic analysis of the polyprotein and 3D sequences indicated that this virus (named duck picornavirus [DPV]) together with porcine enterovirus type 8 virus and several simian picornaviruses form a distinct branch of the family Picornaviridae and should be assigned to a new picornavirus genus.