Knowledge of axillary lymph node status is a key aid to staging and prognosis and it represents a guideline for adjuvant therapy in breast cancer. Despite the morbidity it causes, complete axillary dissection was long the mainstay of treatment. Sentinel lymph node biopsy has proved so reliable in the evaluation of node involvement that axillary node dissection is now generally performed when sentinel node biopsy tests negative. METHODS: In this 3-phase study, 50 patients were enrolled to evaluate the learning curve of sentinel node biopsy (phase 1, September 1997-January 1998); 256 patients (age range 27-81 years) with infiltrative breast cancer (T