Background: Bone marrow transplant (BMT) is used for both neoplastic and nonneoplastic diseases. Following BMT, particularly during the first 3 months, patients have a number of neurologic complications. We evaluated the early neurologic complications following BMT and their influence on survival. Methods: We prospectively followed 115 consecutive patients having BMT for leukemia, for a median period of 90 days after transplantation. Results: Sixty-four patients (56%) had neurologic complications. Sixteen developed more than one complication. Twenty-seven patients (25%) had major neurologic complications: metabolic encephalopathy (8), seizures (8), psychiatric symptoms (3), cerebral hemorrhage (1), cerebral abscess (1), leukemic meningitis (1), peripheral neuropathies (5), and myopathies (2). Forty patients (35%) had minor complications, including headache (16) and tremor(31). Major neurologic complications occurred after engraftment in most patients. Metabolic encephalopathy correlated with graft-versus-host disease(GVHD) (p < 0.03). Seven percent of patients had generalized seizures that occurred without signs of structural cerebral lesions. Probability of survival at day 90 was lower in patients with than in those without major central nervous system complications (63% versus 87.5%, p < 0.01). Conclusions: Neurologic complications are frequent during the first 3 months following BMT and affect patient survival. Drug neurotoxicity and acute GVHD are the main factors influencing their occurrence.