In recent years the identification of mutations and analysis of polymorphisms within the canine genome has been made possible by the introduction of new molecular techniques. The study of alterations in DNA has allowed to better define the correct pathogenesis of mono or multifactorial diseases. In dogs, hereditary diseases defined as congenital if present from birth, can be caused by a single mutant gene and therefore to be transmitted in an autosomal dominant or autosomal recessive manner or to be linked to the chromosome X (sex-linked). However, although it is usually difficult to document in veterinary medicine, also chromosome abnormalities or interaction between multiple genes and exogenous factors may be cause of hereditary diseases. The purpose of this work is to treat those inherited diseases that are recognized in dermatology and for which the genetic defect is known.