The study aimed to evaluate intraoperative immunohistochemistry (IHC) staining of sentinel nodes in primary breast cancer surgery. We analysed retrospectively 1209 consecutive sentinel node procedures and compared the rate of late positive metastases in sentinel node biopsy (SNB) and the duration of the surgical procedures before (n=706) and after (n=503) introducing intraoperative IHC on frozen section. We also did a cost analysis. Intraoperative IHC staining led to a lowering of the late positive SNB rate. Introducing IHC gave a decrease in the late positive rate from 93 to 52% (p<0.0001) for isolated tumour cell metastasis, from 56 to 36.4% (p<0.02) for micrometastasis, and from 16 to 5% (p<0.01) for macrometastasis. The surgical procedures were slightly prolonged for lumpectomies but not for mastectomies after introducing intraoperative IHC staining. The cost analysis showed an overall cost saving of approximately 40%. In conclusion, intraoperative IHC staining of the SNB lowered the late positive rate and gave an overall cost saving.