Overall mortality in the entire group of HSCT recipients during the first 180 days after transplantation was 34.6% (9 of the 26 patients) and the most frequent direct cause of death was acute respiratory distress syndrome (6 patients), in some patients accompanied by sepsis (2 patients), pneumonia (1 patient), or central nervous system (CNS) infection (1 patients). Other death causes included pneumonia (1 patient), bleeding within the CNS during infectious meningitis (1 patient), and shock during subsequent HSCT (1 patient). Seven of the 9 patients died during the first 34 days after HSCT (Table 2 ). In the HHV-6-positive patients, mortality was 50% (5 out of 10 patients). Four of those patients died during the HHV-6 viremia period, which occurred within the first 34 days after HSCT. Table 2 summarizes the clinical features and the times and causes of death of the HSCT recipients.