In 34 patients treated for acute lymphoblastic leukemia (ALL), central nervous system (CNS) damage was assessed by clinical evaluation and brain magnetic resonance imaging (MRI). Twenty-seven of them had been off therapy from 5 to 109 months (median 64 months) while 7 had not completed the maintenance phase of their treatment. All the patients were disease-free when evaluated. None of the 3 patients who showed clinical CNS damage during the follow-up was symptomatic when submitted to MRI, while periventricular hyperintensity in T2-weighted images, suggestive of leukoencephalopathy, was present in 8 of the 34 patients. These subclinical abnormalities appear to be more frequent, transient in nature and treatment-related in patients evaluated shortly after the induction phase. Similar MRI findings seem, on the contrary, to be consequences of the disease on the CNS when appearing in long-term survivors.