We applied fluorescence in situ hybridization (FISH) to assess the presence of structural rearrangement and numerical chromosome aberrations in both metaphase chromosome and interphase nuclei. For this purpose, the biotinylated repetitive alpha-satellite DNA probes for chromosome 1, 18 and 8 (pUC1.77, L1.84 and pJM128) were used to identify tetraploid mosaicism, ring chromosome 18 and trisomy 8 mosaicism for pre-, post-natal and tumor diagnosis respectively. Utilizing this approach, we showed the usefulness of FISH for routine clinical cytogenetics in addition to chromosome banding techniques. The chromosome aberrations with unknown or unclear origin, detected by chromosome analysis, could be confirmed accurately and rapidly.