Effective immunosuppression has improved the results following liver transplantation, but also increased the risk for opportunistic infections. Epstein-Barr virus (EBV) infection in transplant patients can cause various symptoms including the life-threatening premalignant condition, post-transplantation lymphoproliferative disorder (PTLD). Serum specimens from 24 consecutive children (mean 7.6 specimens/patient), who had undergone liver transplantation in Göteborg from January 1995 to May 2002, were analyzed retrospectively for EBV DNA by real-time TaqMan polymerase chain reaction (PCR). The results were related to clinical picture, immunosuppression, graft rejection and infections with other agents. Eleven patients (46%) developed primary EBV infection at a mean time of 4.8 months after transplantation, and six (25%) reactivated EBV infection at a mean of 4.0 months after transplantation. Four of the 11 patients with primary infection had symptomatic EBV infection: two had PTLD and two hepatitis. One patient in the group with reactivated infection developed PTLD. EBV DNA levels were significantly higher in the group with primary symptomatic infection compared with the patients with primary asymptomatic infection (mean 65 500 copies/mL; range 14 200-194 300 vs. 3700 copies/mL; range 100-9780). In patients with symptomatic infection EBV DNA levels did not differ between PTLD and hepatitis patients. The data suggest that quantitative analysis of EBV DNA in serum by real-time PCR is useful for identification of EBV-related disease.