Early-onset autosomal dominant Alzheimer disease (EOAD) is a progressive dementia with reduction of cognitive functions. EOAD presents the same phenotype as sporadic Alzheimer disease (AD) but has an early age of onset, usually before 60 years old. EOAD represents less than 1% of all cases of AD. Initial findings of EOAD are mainly disorders of episodic memory or changes in behavior. The patient is often anosognosic and the diagnosis is therefore carried out with the help of a family member. Neurological signs that can be associated with EOAD are spastic paraparesis, intracerebral hemorrhages, seizures, extrapyramidal syndrome and exceptionally cerebellar ataxia. EOAD is the consequence of either PSEN1 mutations (69%), APP mutations (13%), or APP duplication (7,5%), and exceptionally of PSEN2 mutations (2%). These mutations result in an incompletely understood cascade of events resulting in neuronal death, synapse loss, and the formation of neurofibrillary tangles and senile plaques. EOAD is diagnosed using the clinical criteria of the NINCDS-ADRDA(McKahnn, 1984). Brain imaging can be normal. Lumbar puncture for measurement of cerebrospinal fluid tau and amyloid may be useful (tau and phosphorylated tau are often elevated and amyloid is usually low). Age of onset before 60 years suggests an EOAD and needs a pedigree. Differential diagnosis includes depression and other young dementias such as frontotemporal dementia, Lewy body dementia and Huntington disease (see these terms). Genetic counseling should be offered to the families. Management is symptomatic and includes the use of cholinesterase inhibitors and partial N-methyl-D-aspartate antagonists. Psychotrops may also be useful. The disease is progressive; patients have deterioration in their behavior, cognition, and ability to perform activities of daily living. At an advanced stage, patients are confined to bed.