The autosomal folate-sensitive fragile sites (FS) expression has been analyzed in an autistic children sample and in a control sample. The results obtained have proved that there is a higher frequency of expression of fragile sites in autistic children than in the control sample. The differences are statistically significant. The sex differences level is similar in both groups in relation to fragile sites expression. Three rare fragile sites, 2q13, 6p23, 12q13, are only expressed in autistic individuals. The meaning of these results have been discussed.