Polish avian astrovirus isolates are divided into three groups ( Fig. 1 ): TAstV-1-like, TAstV-2-like and ANVlike. Most of them belong to the TAstV-2 type. These isolates formed two subgroups (subgroups 1 and 2), with the majority being in subgroup 2 (17 isolates). In subgroup 1, three subclades (a, b, c) could be differentiated, and all six Polish isolates clustered in one subclade (a) together with astroviruses previously reported from the USA. Subclade b included strains from the USA, Italy and France that were isolated either from turkey or guinea fowl; however, the latter formed separate sublineages. Subclade c included strains only from the USA. A comparison of nucleotide and amino acid sequences of six Polish turkey astrovirus type 2 strains from subgroup 1, showed 93. 5-99.5% and 96.8-98 .9% similarity to each other and 86.9-91.2 and 93.5-96.8% to the prototype TAstV-2 isolate CA/00. Subgroup 2 TAstVs did not show any distinct subclades and included only European isolates Primer or/and probe positions refer to the sequences for A TAstV-1 (GenBank accession no. Y15936), B ANV Japan/CK/G-4260 (GenBank accession no. AB033998) and C TAstV-2 strain TAstV/CA/00 (GenBank accession no. EU143844) from Poland and Italy. Comparison of a 366-nucleotide region of ORF1b (from nt 4136 to 4502 of the TAstV-2 genome) revealed that, among these isolates, nt identity was between 96.9 and 100%, and deduced amino acid identity was between 97.6% and 100%. In turn, nucleotide and amino acid similarity of this subgroup to the prototype TAstV-2 was 89.5-90.6% and 95.3-96.5%, respectively. Indeed, these isolates formed a separate subgroup, but its distinction was rather weakly supported statistically (bootstrap value 60).