Two cases are reported of a boy and a girl with similar neurocutaneous syndromes clinically characterized by hyperpigmented skin patches and severe CNS involvement. The diagnosis of atypical cases of Incontinentia Pigmenti is suggested. The different syndromes with mental and motor retardation associated with skin abnormalities (Incontinentia Pigmenti, Ito's hypomelanosis, phakomatoses, etc.) are reviewed.