OBJECTIVE The aim of this study was to describe the lymphatic drainage patterns from the 5 "quadrants" of the breast. BACKGROUND Lymphatic mapping has provided techniques to visualize and harvest sentinel nodes in various locations and has generated renewed interest in nodes outside the axilla. METHODS Between January 1997 and June 2002, 700 sentinel node procedures were performed in patients with cN0 breast cancer. Preoperative lymphoscintigraphy was performed after injection of 99mTc-nanocolloid into the tumor in a volume of 0.2 mL and a mean dose of 107.7 MBq (2.8 mCi). Intraoperatively, the sentinel node was pursued with the aid of a gamma-ray detection probe and patent blue dye (1.0 mL, into the lesion). The patients were divided into 5 groups according to the location of the primary breast cancer. In each group, a distinction was made between palpable and nonpalpable lesions of the breast. RESULTS Drainage to either an axillary or an extra-axillary basin was observed in 678 patients. Both palpable and nonpalpable lesions may drain toward the internal mammary chain, although the latter more frequently, regardless of the quadrant. Drainage was also observed to supraclavicular, infraclavicular, interpectoral, and intramammary sentinel nodes. CONCLUSIONS In each quadrant, a breast cancer may drain to sentinel nodes in various locations. There is a distinct difference in drainage patterns between palpable and nonpalpable lesions. These findings may improve the assessment of lymphatic dissemination in invasive breast cancer.