Ectodermal dysplasias (EDs) as defined by Freire-Maia [Freire-Maia (1971); Hum Hered 21: 309–312; Freire-Maia (1977); Acta Genet Med Gemellol 26: 121–131] are congenital disorders characterized by alterations in two or more ectodermal structures, at least one of these involving alterations in hair, teeth, nails, or sweat glands. Suggestions for a new definition and, consequently, for a new classification of EDs have being proposed lately, mainly with the purpose of connecting clinical knowledge with recent discoveries of gene mutations responsible for about 30% of EDs. The aim of this review was to update the clinical classification of EDs with recent molecular (64 genes and 3 chromosome regions) and clinical data, mainly of EDs of the A group (N = 186), in order to contribute information for the evaluation of the ED definition proposed by Freire-Maia. Our conclusion is that the combination of both procedures—clinical and molecular—only brings advantages for a deeper knowledge of EDs. First, it allows a rapid diagnosis that may become even more precise whenever DNA exams are available. Secondly, the comprehension of the biological mechanisms that cause EDs is needed for the design of efficient prevention and treatment approaches. © 2009 Wiley-Liss, Inc.