The human herpes virus 6 (HHV6) is the causal agent of exanthem subitum (rose rash of infants). In addition, however, a wide range of other clinical manifestations are possible, the more common of these include: Untypical exanthem or uncharacteristic rash (with and without fever), acute respiratory disease (ARD) acute gastroenteritis and febrile convulsions (with and without exanthem). More uncommon, and in part unknown, clinical manifestations associated with HHV6 infection are discussed in Part 2 of this paper. In common with other herpes viruses, HHV6 also tends to show persistence and intermittent or chronic shedding in the normal population, making the unusually early infection of children (seroconversion in the first year of life in up to 80% of all children) understandable. This means that HHV6 infections manifesting in close temporal association with recommended vaccinations may be misinterpreted as complications of the vaccination. Today, the situation can be clarified by employing special virological-serological laboratory tests, which are available throughout the country.