Background. The feasibility and accuracy of immunohistochemistry (IHC) on frozen sections, when assessing sentinel node (SN) status intraoperatively in breast cancer, is a matter of continuing discussion. In this study, we compared a center using IHC on frozen section with a center not using this method with focus on intraoperative diagnostic values. Material and Methods. Results from 336 patients from the centre using IHC intraoperatively were compared with 343 patients from the center not using IHC on frozen section. Final evaluation on paraffin sections with haematoxylin-eosin (HE) staining supplemented with cytokeratin staining was used as gold standard. Results. Significantly more SN with isolated tumor cells (ITCs) and micrometastases (MICs) were found intraoperatively when using IHC on frozen sections. There was no significant difference in the number of macrometastases (MACs) found intraoperatively. IHC increased the sensitivity, the negative predictive value, and the accuracy of the intraoperative evaluation of SN without decreasing the specificity and positive predictive value of SN evaluation. Conclusions. IHC on frozen section leads to the detection of more ITC and MIC intraoperatively. As axillary lymph node dissection (ALND) is performed routinely in some countries when ITC and MIC are found in the SN, IHC on frozen section provides valuable information that can lead to fewer secondary ALNDs.