Pilar dysplasias are congenital or acquired disorders, they are characterized by hair abnormalities in color, density, length and structure. Optic microscopy and polarized light microscopy analysis of piliary shafts provides important informations and contribute to the diagnosis of complex syndromes. Many pathological profiles can be visualized, some are specific, other are not. Some authors use a particularly convenient classification including 3 groups: in the first, piliary shaft abnormalities are isolated, in the second the abnormalities correspond to complex syndromes, and in the third they are associated with various malformations. Based on some clinical cases, we will describe various types of pilar dysplasias and we present recent advances, particularly in genetics.