Fahr’s disease (FD), also known as familial idiopathic basal ganglia calcification, is a neurodegenerative disease affecting cerebral microvessels, mainly in the basal ganglia. It mostly presents with movement disorders, dementia and behavioural abnormalities. It is considered hereditary with an autosomal dominant transmission. Fahr’s disease is often underestimated and underdiagnosed. We describe a rare case of Fahr’s disease: it manifested itself with cognitive and behavioural alterations in absence of extrapyramidal disorders. Diagnosis was supposed only after CT scan. Since onset of FD may only present with cognitive dysfunction without extrapyramidal signs, physicians should consider this complex syndrome when consulting patients with mental deterioration and behavioral abnormalities. Neurological and psychological examinations and CT imaging remain the basic techniques for the diagnosis of Fahr’s disease.