OBJECTIVE To investigate lymphatic drainage as measured by lymphoscintigraphy in the arms of patients undergoing either sentinel lymph node biopsy (SNB) or axillary lymph node dissection (ALND). METHODS From January 2001 to December 2002, 30 patients with unilateral invasive breast carcinoma underwent breast-conserving surgery with SNB and 30 patients with ALND. All patients received radiotherapy to the breast. Lymphoscintigraphy was performed, and skin circulation, skin temperature, and arm volume were measured 2-3 years after radiotherapy. RESULTS None of the 30 patients who underwent SNB showed any clinical manifestation of lymphedema. Of the 30 patients undergoing ALND, six (20%) had clinical lymphedema, with an arm volume that was >10% larger on the operated than on the non-operated side (P<0.01). Scintigraphically, visual analysis revealed lymphatic dysfunction in three patients, manifested as forearm dermal back flow. Two of these patients also had an increased arm volume. Quantitative analysis showed no differences between the groups, apart from a smaller amount of isotope in the axilla in the ALND group. There was no difference in skin circulation or skin temperature. CONCLUSIONS Our study shows that lymph drainage in the operated arm compared with the non-operated arm was less affected by SNB than by ALND, and that morbidity associated with SNB was lower than with ALND. However, the results do not confirm our hypothesis that lymphoscintigraphy can reveal differences in lymph circulation that are not evident clinically in the form of manifest lymphedema. The most sensitive clinical method of assessing lymph drainage seems to be measurement of arm volume.