Infantile-onset leukoencephalopathy of van der Knaap type is manifested by initially normal or near normal neurological findings despite infantile-onset megalencephaly and magnetic resonance imaging evidence of severe white matter affection. Until this entity was recently described, these cases were usually presented under the heading of atypical variants of Alexander disease. To date 63 individuals have been reported in English literature. We report a four-year-old boy presented in the first months of life with progressive megalencephaly. delay in walking, clumsiness, convulsions and magnetic resonance imaging evidence of diffuse swelling of white matter, cystic cavitations in frontal, temporal and parietal lobes. (C) 1999 Elsevier Science Ltd. All rights reserved.