To screen a selected group of children with idiopathic mental retardation for subtelomeric abnormalities using the fluorescent in situ hybridization (FISH), which has been reported to be cost-effective in routine applications. We also aimed to assess the availability of the scoring system which is used for selection of those children for FISH analysis. A total of 30 children aged 3-16 years with idiopathic mental retardation (moderate to severe) and normal karyotypes were included in this study. The children whose parents had consanguineous marriages were excluded from the study. All cases were evaluated using the scoring system published by de Vries et al. (5) Forty-one subtelomeric regions for each case were analyzed by fluorescent in situ hybridization. One case with a score value 5 presented terminal deletion of chromosome 9p by FISH (3.3 %). Analyzing chromosomes of the same case with higher resolution G-banding showed the same abnormality. The frequency of subtelomeric abnormalities in our study group was much lower than the frequencies reported in other studies and the scoring criterions suggested by de Vries et al. have not effectively increased our subtelomeric deletion detection rates. Autosomal recessive disorders may be a more common reason compared to subtelomeric abnormalities in this group of patients in the countries where consanguinity rate is high. Laboratories may be encouraged to analyze high-resolution G-banded karyotypes in those cases. Moreover more effective selection criteria for FISH are suggested by establishing thorough genotype-phenotype correlations besides case reports with different subtelomeric abnormalities.