Forty patients suffering from neuronal ceroid lipofuscinosis, 33 of the juvenile type (JNCL) and 7 of the infantile type (INCL), underwent a brain CT. All INCL patients showed severe atrophic changes which were most pronounced supratentorially and in the brainstem. The white matter was hypodense and markedly reduced and the cortical gray matter was quite thin in the oldest patients. The CT signs appeared early and can be used in differential diagnosis. In the JNCL group, CT findings were normal under the age of nine, but in the older patients (n = 28) atrophic changes were detected in all but two. Both supra- and infratentorial atrophy was detected and the severity of the alterations increased with age. No abnormal densities in the brain parenchyma were detected on CT. The severity of the cerebellar atrophy correlated positively with disturbances in motor functions, balance, co-ordination and EEG.