Risk factors for hepatic veno-occlusive disease (HVOD) were analysed in a population of 136 autografted children who received high-dose busulfan (BU) as part of a conditioning regimen. HVOD was diagnosed according to McDonald's clinical criteria. The incidence of HVOD was particularly high in this series (22%) compared with series with other conditioning regimens but the outcome was favorable in 26 patients (87%). Four deaths occurred (13%), one of which was HVOD related. The clinical presentation of HVOD was similar to that described in previous reports. Although statistical analysis failed to demonstrate any factors predictive of outcome, it did identify risk factors for the occurrence of HVOD: these were (1) a total dose of BU exceeding the standard 16 mg/kg dose; (2) the use of three as opposed to two alkylating agents; (3) the sequence of BU administration when given in the conditioning regimen containing three alkylating agents; and (4) concomitant ketoconazole therapy.