Tumor size correlates with lymph node metastasis in breast cancer. In multifocal lesions there is controversy about considering the summation of the largest diameter of each tumor. A total of 122 patients with multifocal breast cancer were compared in a retrospective study with 177 patients with unifocal tumors, correlating tumor size with lymph node metastasis. In multifocal tumors, two sizes were considered: the diameter of the largest tumor and the combined diameter of all lesions. Relationship was established by three different logistic models using variables such as age, number of lesions, histologic type, and grade. At a same size of the largest diameter of a unifocal or multifocal lesions and the combined diameter of a multifocal lesion, the latter shows less probability of nodal metastasis indicating that combined diameter is an overestimation of the lesion size. Our results indicate that in multifocal breast cancer, only the diameter of the largest tumor breast cancer has relationship with lymph node metastasis.