Seventy-five children aged less than 3 yrs, affected by Roseola infantum (maculopapular rash following an acute onset illness characterized by high fever for 2-5 days) were included in this study, 40% of them were admitted with urgency to our clinic for febrile convulsions. Several bacterial or viral agents other than HHV6 were isolated from more than 10% of the children; the role of HHV6 was studied with an immunofluorescence test (IFA) for specific antibodies (seroconversion); 25 single serum samples of the acute phase and 30 acute and convalescent paired sera were available; high positivity was shown in three preexanthematous samples; a serological evidence of HHV6 infection was obtained in only 9 of the 30 paired sera; a coinfection was shown in two subjects belonging to the last group; viral or bacterial agents other than HHV6, were demonstrated in 4 seronegative children. In our experience, the etiologic role of HHV6 in exanthema subitum is not always confirmed; we cannot explain the controversy of our results compared with those of Japanese literature.