Adenovirus infection remains an important cause of mortality after bone marrow transplantation (BMT). Currently no efficient antiviral treatment is known. Thus, testing new modalities of early diagnosis and treatment is a crucial objective. Adenovirus infection is defined by the combination of symptoms and the isolation of virus from the source of clinical symptoms. The involvement of two or more organs and the presence of virus in blood cultures define disseminated disease. Seven children with a median age of 7 years received bone marrow transplantation for leukemia. All received an unrelated graft without T cell depletion. Adenovirus was sought in blood, urine and biopsy specimens using PCR and culture. Analysis of biopsy specimens included systematic immunohistochemistry. Cidofovir treatment was initiated as soon as biopsy revealed the histopathological signs of adenovirus. Cidofovir was given at 5 mg/kg once weekly for 3 weeks then every 2 weeks. Six patients had diarrhoea and one patient had cystitis. Adenovirus infection and disseminated disease were diagnosed in four cases and three cases, respectively. In six cases, serotype A31 was isolated from gastrointestinal biopsy and in two cases serotypes B2 and C6 were detected in blood and urine. Cidofovir treatment was associated with clinical improvement of diarrhoea, cystitis and fever in five patients, in whom the virus became undetectable in cultures and PCR analyses despite the persistence of immunodeficiency. The median follow-up was 360 days after BMT (240-570). One child died of invasive aspergillosis and another of disseminated adenovirus after interruption of cidofovir therapy. Further studies in immunocompromised patients will be needed to extend these promising results concerning the role of cidofovir in adenovirus infection.