Idiopathic thrombocytopenic purpura (ITP) in children is usually triggered by a viral infections such as cytomegalovirus (CMV) or Epstein-Barr virus (EBV) infection. The aim of this study was to assess the frequency of CMV and EBV infections in children with first relapse of ITP, and the influence of these infections on the course and response to treatment of ITP. Sixty patients (30 boys and 30 girls) with ITP were enrolled into the study. We found that the age at the onset of ITP was from 1 month to 17 years (mean 7.0 ± 5.7 years), the platelet number was from 1 to 79 x 10(9)/L (mean 18.1 ± 19.0 x 10(9)/L) at the time of diagnosis and it increased from 17 to 395 x 10(9)/L (mean 134.4 ± 81.2 x 10(9)/L)(p < 0.05) after the first course of therapy. Forty seven patients required pharmacological treatment, the duration of the treatment was from 2 to 25 days (mean 6.1 ± 4.1 days). Relapses were observed in 27 (45%) of the patients. Active CMV infection was found in 19 patients (31.7%), EBV infection in 5 patients (8.3%), and both infections concomitantly in 1 patient (1.7%). The group of patients with CMV or EBV infection(n = 25) did not differ from the patients free of infection (n = 35) in regard to the age, number of platelets at onset, duration of treatment, number of platelets after treatment, number of relapses, and the interval between the onset and first relapse. In conclusion, active CMV or EBV infection is common in children with ITP. These infections do not seem to have an appreciable bearing on the clinical course and the response to treatment on children with ITP.