Fluorescence in Situ Hybridization (FISH) is a molecular cytogenetic technique that uses fluores-cent probes which bind to specific chromosomal locations within the nucleus to search and detect chromosomal abnormality. In the last decade, tumor-specific chromosomal translocations, deletions, gains, amplifications, and novel oncogenes have become increasingly important in the field of diagnostic, therapeutic, and prognostic concepts in medicine. FISH technique provides a quick analysis of formalin-fixed paraffin-embedded cells which can be used in daily practice of pathology for several tumor types. Fluorescence in Situ Hybridization (FISH) technique is based on hybridiza-tion of tagged DNA probes which are fluorescent reporter molecules that affirm the presence or absence of particular genetic anomaly under fluorescence microscopy. This technique has been recently developed to screen the whole genome coexistently through multicolor whole chromosome probe techniques that multiplex-FISH or spectral-karyotyping or through an array-based method using comparative genomic hybridization. The aim of this article was to provide a theoretical survey of FISH for clinical function in surgical pathology habit.