The main peculiarities of the hypomelanosis of Ito (HI) or incontinentia pigmenti achromians are shown. The most frequent and severe complications of this multisystemic neurocutaneous disease are reviewed. The most severe complications concern to the central nervous system (CNS), mental retardation and epilepsy--both present in more than 50% of cases--being the two most severe and frequent disorders. About 10% of patients with HI show infantile spasms during the first year of life and another 10% have autistic behavior. Moreover, other complications can be observed in some patients. These complications consist of ocular, musculoskeletal and oral alterations, hypotonia, macrocephalia, microcephalia, congenital cardiac malformations, urological and genital malformations and other rarer disorders. Chromosomal anomalies, especially translocations or mosaicisms type are found in about 50% of cases. The study, however, can show the chromosomal abnormalities in the karyotype performed in fibroblasts of the hypopigmented skin while it may be normal in the blood and in skin unaffected.