The main purpose was to discover how frequently Mexican criminals exhibit the XYY chromosome complement and to establish the physical traits associated with this abnormality, especially above-average height. Of 236 inmates tested, 233 showed normal chromosome complements. None of the remaining 3 was an XYY carrier, but 1 of them had 47 chromosomes in all the cells analyzed and an XXY karyotype, while the other 2 showed the anomaly of chromosome division called chromosome mosaicism. The XXY carrier's height was slightly above average and that of the two mosaic carriers was considerably above average when compared to that of their fellow inmates. The absence of the XYY chromosomal abnormality in this entire prison population may be explained at least partly, by the nonserious nature of their committing offenses (the penitentiary studied is not a maximum-security facility). The inmates' acts can be explained by socioeconomic factors, rather than by genetic instructions. Further studies with similar populations are needed. An English and French abstract are provided and 7 references are appended. --in Spanish.