Summary:Neurological complications may occur in BMT recipients (11-59%), frequently contributing to morbidity or mortality. They are the main causes of death in 10-15%. Lifethreatening neurological complications were seen in 11 out of 113 (9.7%) children who underwent BMT from HLAmatched family (n ¼ 7) or mismatched donors (n ¼ 4) at our institution. Diagnoses of patients with neurological complications were acute myeloblastic leukemia (AML) (five), thalassemia major (two), Fanconi anemia (two), Omenn syndrome (one) and leukodystrophy (one), and the neurological events were seen between days þ 13 and þ 85 after transplantation. Minor symptoms including reversible, nonrepetitive seizures were excluded. Cyclosporine A toxicity was diagnosed in six children. The rest of the complications were brain abscess/meningoencephalitis (two), severe hypomagnesemia (one), busulfan toxicity (one), sustained hypertension (three), and intracranial hemorrhage (three). Six patients with neurological complications suffered from 4grade II graft-versus-host disease (GvHD), and all were high risk for transplantrelated complications. In this study, risk status of the underlying disease, mismatched transplantation, a diagnosis of AML (advanced stage), older age and 4grade II GvHD were important adverse factors for the development of severe life-threatening neurological complications. Bone Marrow Transplantation (2005) 35, 71-76.