SUMMARY Introduction. Posterior cortical atrophy (PCA) is a focal dementia manifested by posterior cognitive disorders, initially visuoperceptual alterations due to damage in occipito-parietal cortex, which permits PCA to be clinically differentiated of Alzheimer's Disease (AD). Objetive. To analize and to compare cognitive performance of patients with PCA and with AD. Materials and methods. Sample was conformed by the following groups: four patients with PCA, seven with early familial AD, nine with late sporadic AD and four healthy controls. A neuropsychological examination battery was administrated to each participant in order to assess cognitive processes and functionality. Between-groups comparisons were made by using U Mann-Whitney non parametric test. Results. Patients with PCA had significantly lower scores in constructional and ideational praxias, reading, calculation and visuoperception, compared to both AD groups. In contrast, PCA group showed better performance in verbal memory, semantic fluency and executive function. Conclusion. At the beginning of neurodegenerative process, PCA symptomatology is clearly different of that presented in AD. PCA is a dementia with particular symptomatic characteristics and not only a variant of AD, even if both share the same hystopathological substrate.