The size of the breast tumor is relevant in a patient s management also affecting the prognosis. For unifocal lesions, tumor staging depends on the maximum diameter of the tumor, whereas in multiple lesions, this issue is not standardized. The aim of this paper is to study which is the best method in the assessment of the tumor size in multiple invazive carcinomas (multifocal and multicentric) in correlation with the lymph node metastases developement. Two different assessments of the tumor size (diameter of the largest focus=LD, and combined, aggregate diameter of all the foci=AD) were used in 418 primary invasive breast lesions (91 multiple, 327 unifocal) and compared with the nodal status (CHI-test). The use of combined tumor focus upstaged 23 (25.27 %) patients with multiple tumors (16 upstaged from pT1 to pT2 and 7 from pT2 to pT3). There was no difference in nodal positivity based on pT status between LD and AD. We observed a statistically significant difference in the mean diameter of the largest focus between the unifocal and multifocal group (31,47 vs 39,67 mm) (p=0,0013). Aggregate diameter in multiple breast cancer is not correlated with an increase of axillary metasases and should not be used for staging.