Thirty-one children with developmental delay and associated dysmorphic features were selected from the Genetics Clinic of Cairo University Children’s Hospital. G-banded karyotype using Giemsa stain was done for all patients which showed apparently normal karyotype except for three cases; the first case showed 15p+, the second showed pericentric inversion of chromosome 19 in one metaphase and the third case showed trisomy 16 also in one metaphase. FISH technique using the human pan telomere probe was performed for all children. According to the telomere signals viewed with fluorescence microscope during interphase, the patients were divided into two groups, the first group 22 cases (71%) showed signals that ranged from 22 to 33 (mean signals 28), and the second group 9 cases (29%) gave signals between 3 to 11 (mean signals 8). Because of the marked difference in telomere signals between the two groups the second group was considered as the group with telomere loss.