Background: Fahr s disease (basal ganglia calcification) is characterized by bi hemispherical calcium deposition in basal ganglia, dentate nucleus and semioval center. Its clinical manifestations are a rigid hypokinetic syndrome, mood disorders and cognitive impairment. Aim: To report to the results of a neurological assessment of three siblings with Fahr disease. Patients and methods: Three sisters, aged 55, 56 and 58 years, were studied. All had a rigid hypokinetic clinical picture associated with cerebellar involvement and a cognitive impairment that progressed in 8, 6 and 10 years respectively. Brain CAT scans showed symmetric and extensive calcifications of cerebellar white matter and dentate nuclei, pons, mesencephalon, lenticular nuclei, thalami and semioval centers. Hypoparathyroidism was ruled out. Cognition was assessed with WAIS and Benton tests and Weschler memory scale. The time of reaction to visual stimuli was studied. The processing speed of visual information and the interhemispheric conduction time of such information, were calculated. Cognitive evoked potentials (P 300) were also studied. Results: Cognitive impairment involved verbal and visual-spatial memory, planning, attention and concentration capacities and visual constructive skills. There was a prolongation of reaction time latencies and loss of the normal asymmetry of interhemispheric transmission (without right to left facilitation). P 300 evoked potentials were absent. Conclusions: These observations suggest that the pathogenesis of cognitive and motor changes in Fahr s disease is based in a dysfunction of cortico basal connections and their interhemispheric relations. This defines a subcortical dementia secondary to mineral deposits in subcortical structures ( Rev Méd Chile 2002; 130: 1383-90).