PURPOSE: The objective of arm sentinel lymph node (SLN) detection were to identify the presence of different drainage tracts of the breast and arm lymphatics and eventually to prevent lymphedema after an axillary procedure. METHODS: Twenty one patients underwent surgery for breast cancer, with arm SLN detection, from March to July 2008 at Samsung Medical Center. We used the (99)Tc-tin colloid isotope in two patients, blue dye in 18 and green dye in one for the arm SLN detection. RESULTS: Stained and/or hot nodes from the arm lymphatics were identified in 15 of the 21 patients (71.4 %). Among the 15 patients who had the arm SLN identified, one patient had a metastasis at the arm SLN, and another patient had common breast and arm lymphatic drainage. CONCLUSION: Identification of the arm lymphatic drainage was possible. Since there were cases of common pathway of the arm and breast lymphatics and metastasis of the arm SLN, we cannot conclude that the arm SLN detection was safe and effective. A subsequent study for identifying the presence of two different drainage systems of the breast and arm lymphatics and confirmation of no metastasis at the arm SLN is needed.