We have sequenced the genomic 3′-end, including the structural gene, of human astrovirus (HAstV) serotype 7 and morphologically related viruses infecting pig (PAstV), sheep (OAstV) and turkey (TAstV-1). These sequences were compared with corresponding astrovirus sequences available in the nucleic acid databases, including sequences of the seven other HAstV serotypes, two other avian astroviruses (TAstV-2 and avian nephritis virus) and astrovirus from cat (FAstV). A 35 nt stem–loop motif near the 3′-end of the genome, previously described as being highly conserved, was present in all of the astroviruses except TAstV-2. In the N-terminal half of the capsid precursor protein, there were several short conserved peptide motifs. Otherwise the capsid proteins of astroviruses infecting different hosts were highly divergent. Calculation of genetic distances revealed that the distance between FAstV and HAstV is comparable to the largest distances between different HAstV serotypes. Higher similarities between the HAstV, FAstV and PAstV capsid sequences suggest interspecies transmissions involving humans, cats and pigs relatively recently in the evolutionary history of astroviruses.