Besides its typical amnesic presentation, focal atypical presentations of Alzheimer’s disease (AD) have been described, such as frontal variant. It’s a rare phenotype described in patients presenting prominent behavioural deficits. Three patients were diagnosed with frontal variant of AD. The age at onset of symptoms was 80 years. At the onset of the disease, all patients had predominantly inert behavior presentation. Neuropsychological tests showed impairment in global cognitive efficiency (MMSE 15/30). There was an episodic memory deficit characterized by a low free recall (free recall score = 1/10) not normalized with cueing (total recall = 1/10). Mental flexibility and the abilities of conceptualizing and programming were severely impaired on the copy of Rey complex figure. Dysexecutive deficits were present in all patients (BREF Test = 8/18). One patient presented gestural apraxia. Verbal fluencies were reduced, both in phonemic (score = 2/28) and categorical modalities (score = 2/28). Our patients were evaluated with the NPI. All of them had severe behavioral and psychological Symptoms (Global score = 44/ 144). Brain SPECT showed hypoperfusion in dorsolateral prefrontal cortex. CSF biomarkers showed low Aβ42 (329 pg/mL), high Tau (1073 pg/mL) and high P-Tau (97 pg/mL), in favor of an AD diagnosis. Frontal variant of AD is a rare form in which patients present severe behavioral and psychological Symptoms. By using physiopathological markers, such as CSF markers, it is now possible to establish a biological diagnosis of AD in these focal cortical syndromes, and to propose a specific treatment for them.