The adult-onset autosomal dominant leukoencephalopathies are rare disorders. Very few pedigrees have been extensively described and no biochemical or genetic marker has been identified so far. The present study was aimed to characterized an autosomal dominant late-onset leukoencephalopathy occurring in a large Italian kindred. A genealogic method was adopted to ascertain 51 affected individuals among nearly 400 subjects in 8 generations. Medical records were obtained from 11 deceased patients. We personally examined 8 symptomatic and 9 asymptomatic at-risk individuals who underwent a standardized clinical, biochemical, radiological and neurophysiological study. The mean age at onset of the disease was 46.6 years and the mean duration of disease 9.9 years. The clinical picture was characterized by progressive pyramidal and pseudobulbar signs, urinary incontinence and, sometimes, action tremor of the head and/or hands. No relevant mental deterioration was noted. In all the symptomatic and in 1 asymptomatic subject, brain MRI showed marked symmetrical hyperintensity on T2-weighted images of the white matter of the cerebral hemispheres, with constant sparing of the cerebellum. In these subjects, evoked potentials revealed altered central neural conduction. Nerve conduction velocity, biochemical (including lysosomal enzymatic activities) and biopsy (peripheral tissue specimens) examination were normal. The clinical and neuroradiological data are consistent with an autosomal dominant adult-onset leukoencephalopathy whose features are unusual when compared to those previously reported.