Immunohistochemistry (IHC) is the application of antibody methods to slide-based material i.e. cells and tissues. No other technique has so revolutionised the field for the past 50 to date. IHC has become a staple of the histopathology laboratory. The advantages of this technique are obvious: it is simple, fast and cost-effective. IHC is of great help in oncology: to classify a tumor in its category, to identify the origin of a metastasis and in some cases to establish the malignancy of a lesion. The implications of IHC in the determination of prognostic and predictive factors in oncology are still limited, but start to develop, particularly in the field of the detection of hormon receptors and of the overexpression of HER2/neu in breast cancer. Although IHC lacks of reproducibility, the development of quality assurance programs will contribute to the development of IHC in predictive oncology.