Exanthem subitum (ES) is a common childhood exanthematous disease. In a recent study of ES due to human herpesvirus 6 (HHV 6), we isolated human herpesvirus 7 (HHV 7) from the peripheral blood mononuclear cells (PBMC) of a seven month-old infant with typical symptoms of ES. The identity of the virus was confirmed by indirect immunofluorescence using HHV 7 specific monoclonal antibody and by amplification of the HHV 7 specific genomic sequences using the polymerase chain reaction (PCR). Paired serum samples from the infant showed serological conversion to the isolated virus. The clinical manifestations of ES in this infant appeared to be milder than the classical ES due to HHV 6.