OBJECTIVE In HIV-1-infected children, active cytomegalovirus (CMV) infection can cause severe clinical manifestations and accelerate progression of HIV disease. However, sufficient quantities of blood samples may not be available either for culture or detection of CMV DNA or antigens in white blood cells. The aim of this study was to investigate the diagnostic and prognostic significance of detecting CMV DNA in serum samples from HIV-1-infected children. METHODS Sera from 55 children (18 boys), aged 2-130 months (mean, 49.8 months), with perinatal HIV-1 infection and clinical manifestations attributable to CMV infection were tested for CMV DNA by nested polymerase chain reaction and for class-specific CMV antibodies [immunoglobulin (Ig) G, IgA, IgM] by enzyme-linked immunosorbent assay. The children were followed up for 2 days to 59 months (mean, 25.5 months). RESULTS CMV infection was demonstrated in 43 children (74.5%), 18 of whom (42%) were positive for CMV DNA. During the follow-up, 13 children with CMV infection (30.2%) died, including 11 (84.6%) who were positive for CMV DNAemia just before death. Of these children, seven died soon after hospitalization without antiviral treatment, and four died despite therapy with ganciclovir or foscarnet. Post-mortem CMV inclusions were revealed in seven out of eight children who underwent autopsy. The two other children who died also had progressive CMV disease and received ganciclovir until death. In comparison with CMV-seropositive children without CMV DNAemia, children with CMV DNAemia showed significantly shorter mean survival time (42.5 versus 60 months; P < 0.01), lower final CD4+ T-cell count (218 versus 499 x 10(6)/1; P < 0.01) and higher mortality rate (P < 0.0001). CONCLUSIONS The detection of CMV DNA in serum is of value for diagnosis of active CMV infection in HIV-1-positive children, and CMV DNAemia is a good prognostic indicator of severe outcome of HIV disease.