In the last decade sentinel lymph node biopsy has become a well-established method for axillary lymph node staging in patients with breast cancer. Using preoperative imaging modalities it can be tested whether patients are suitable for sentinel node biopsy or if they should directly undergo an axillary dissection. The imaging modalities used must be mainly characterized by a high positive predictive value (PPV). For this question B-mode ultrasound is the best evaluated method and provides clear morphological signs for a high PPV (>90%) but the sensitivity barely exceeds 50%. It has not yet been proven whether other modalities such as duplex sonography, magnetic resonance imaging, computed tomography (CT) or scintigraphy might achieve a higher sensitivity while still maintaining a high PPV. There is only some evidence that positron emission tomography (PET) might achieve a higher sensitivity. This should be confirmed by further studies because PET or PET/CT will play an increasing role for an initial whole body staging in patients with breast cancer in the near future.