We review the evidence for the frequency of the fragile X syndrome (FXS), other X-linked abnormalities, and other chromosomal disabilities of Turkish pediatric psychiatry outpatients with intellectual disability. Reported clinical features and genetic findings were used in cytogenetic screenings to estimate the prevalence of the fragile X (fra X) and other chromosomal aberrations in 120 patients with mental retardation, language disorders, attention deficit hyperactivity, or developmental delay, in comparison with 30 healthy children. Data on the clinical, intellectual and behavioral findings in 14 fra X positive children (11.7%) is presented. Ten of the 120 patients (8.3%) had enlargement of the heterochromatin region of chromosome 9. Other chromosomal aberrations and autosomal fragile sites (FS) were also observed. There was a statistically significant difference in the autosomal and X-linked FS between the study and control groups (p<0.05). The tests for the fra X chromosome are likely to be of diagnostic benefit in young children with autism or developmental delay, particularly in speech, and who have large and prominent ears.