Prolongation of survival in patients with breast cancer due to early diagnosis and modern methods of treatment has turned the attention on lymphedema, which is the most important morbidity secondary to the treatment of the disease. Determination of lymphedema and related risk factors in patients before a surgical intervention may provide protection for patients and early treatment. The aim of this study was to determine the presence of lymphedema before surgery by bioimpedance analysis in patients with breast cancer and to establish risk factors associated with lymphedema. A total of 277 patients who were diagnosed as having breast cancer, were planned to undergo a surgical intervention, and had no clinical lymphedema were included in the study. The presence of lymphedema was evaluated with clinical examination, measurement of arm circumference, and bioimpedance analysis. Lymphedema was found in 59 (21.3%) patients with no detected differences in arm circumferences. A significant relationship was found between the presence of lymphedema and body mass index (BMI), number of positive lymph nodes, and capsule invasion of the tumor (p = 0.001, p = 0.003, p = 0.002, respectively). Multiple regression analysis revealed that BMI and the number of positive lymph nodes were independent variables (p = 0.024, p = 0.002). ROC curve analysis resulted in an increased risk of preoperative lymphedema when the number of positive lymph nodes was ≥8. Correlation analysis revealed a positive correlation between the number of positive lymph nodes and L-dex score (p = 0.001, r = 0.219). Preoperative bioimpedance analysis demonstrated that ∼1/5 of the patients had subclinical lymphedema. Preoperative subclinical lymphedema is associated with obesity and the number of positive lymph nodes, and thus, treatment of the axilla in patients who are preoperatively detected to have subclinical lymphedema should be revised.