The aim of the study was to assess the accuracy of a real-time quantitative RT-PCR (qRT-PCR) assay for mammaglobin 1 mRNA in the detection of metastatic breast cancer in axillary sentinel lymph nodes (SLN), comparing the results with those of qualitative RT-PCR assays and of an extensive histopathological examination. A retrospective series of 81 SLN from 72 patients and a validation series of 61 SLN from 61 patients were evaluated. In the retrospective series, the qRT-PCR assay was positive for 23 (28.4%) of the 81 SLN. The overall concordance with histopathology was 93.8%, with a sensitivity of 90.9%, a specificity of 94.9%, a positive predictive value (PPV) of 87% and a negative predictive value (NPV) of 96.6%. In the same series, qualitative RT-PCR showed an overall concordance with histopathology of 86.4%, a sensitivity of 72.7%, a specificity of 91.5%, a PPV of 76.2% and a NPV of 90%. In the validation series, including 23 patients with pure in situ carcinoma, the real-time qRT-PCR assay showed an overall concordance with the histopathologic findings of 93.4%, with a sensitivity of 75.0%, a specificity of 94.7%, a PPV of 50.0% and a NPV of 98.2%. We conclude that real-time qRT-PCR assays for mammaglobin 1 are more sensitive and specific that qualitative RT-PCR assays for the detection of metastatic breast carcinoma in axillary SLN, but it should not be regarded as a possible substitute for an extensive histopathological scrutiny of the SLN in the clinical practice.