In situ hybridization: Introduction to techniques, applications and pitfalls in the performance and interpretation of assays

•In situ hybridization(ISH) has become a common laboratory technique used for the analysis of gene expression and for the localization of specific DNA and RNA molecules in cells.•These techniques have evolved into important tools in basic scientific research and in clinical diagnoses.•Because of the possibility of false positive and false negative results that may occur with ISH assays, familiarity with the pathophysiology of the molecules that are analyzed and the cellular processes involved as well as with limitations of the assays can help to avoid erroneous diagnoses with clinical specimens.