This report describes classical Type 1 insulin deficient diabetes mellitus (DM) arising in twins aged 14 months, both of whom had evidence of enterovirus infection. The diagnosis of Type 1 DM was made in the second twin within 12 days of the first. Enterovirus infection was detected in each twin at diagnosis by polymerase chain reaction (PCR). Both twins were negative for enterovirus by PCR 5 months following diagnosis, although both were then positive for islet cell antibodies. Sequencing of the amplicons produced by PCR suggested that the viruses from each twin were not the same but that they were both variants related to echovirus 6.