Specific IgG antibodies against BK virus measured by ELISA were used as a marker of previous infection. Results with sera from healthy people of different counties in Portugal were compared with previous findings in Norwegian sera. No significant difference between the prevalence and level of BKV IgG could be found between Portugal and Norway, and when comparing the different counties of Portugal. Thus, the way of transmission seemed to follow the same routes both in rural and urban counties in Portugal, and in Norway.