The objective of this study was to evaluate the accuracy of bioimpedance spectroscopy measurements (L-Dex) in the diagnosis of breast cancer-related lymphedema. A retrospective review of a prospectively maintained database was performed of all patients that underwent surgical treatment for breast cancer at a tertiary medical center. Patients who had preoperative and postoperative evaluation for possible lymphedema by limb circumference measurements and bioimpedance were eligible for inclusion in the study. No significant demographic differences were found between the group of patients clinically diagnosed with lymphedema (N=134) and those without a clinical diagnosis of lymphedema (N=261). The ability of bioimpedance to diagnose lymphedema based on the manufacturer's criteria demonstrated low sensitivity, which was 7.5% when lymphedema was defined as an absolute L-Dex value greater than 10, and 24.6% when defined as a relative change of >10 between preoperative and postoperative measurements. This corresponded with a positive predictive value of 61-71% and a negative predictive value of 67-70%. We are unable to recommend the use of bioimpedance as a screening tool or for measurement of breast cancer-related lymphedema.