Mutations or chromosome aberrations are considered alterations in the chromosome number or structure. They are mainly considered due to gametogenesis inborn error (meiosis) or during the zygote first cellular divisions. All these alterations might be observed during metaphase from the cellular cycle, where DNA loses are seen (clastogenic processes) due to DNA repair processes deficiency o total absence, among others. 4617 chromosomal studies were performed at Hospital Para El Nino Poblano (Pediatric Hospital) in Mexico. During 19 years period of time (from 1992 to 2011) were 34.6% (1596 patients) showed different chromosomal alterations. Among the studies population, male and female pediatric patients with different genetic diseases were chosen. These chromosome changes are classified as numeric or structural alterations, respectively. Another group of genetic alterations are known as mutations and can be inherited among generations. A wide variety of pediatric patients with genetic diseases due to chromosome aberrations are described in this study analyzing their clinical characteristics, medical or surgical treatments and their medical evolution according to the genetic disease. Key words: Chromosome, mutation, chromosome aberration, numeric and structural changes, karyotype and DNA