Our data prove that TT virus is efficiently transmitted transplacentally. The increase of its prevalence in the group of newborns older than 1 week suggests that it may be furthermore transmitted postnatally. Therefore in our Caucasian population, vertical transmission, particularly in utero transmission, of TTV is likely to account for a major part of TTV infection in early childhood. However, no disease activity could be established for the novel virus by this infection route.