OBJECTIVES:The study aimed to investigate the positive predictive value (PPV) of mammographic lymphography (MLG) for assessing malignant breast disease and lymphatic metastasis in patients in a typical clinical setting. MATERIALS AND METHODS:Patients who underwent mammography with Breast Imaging Reporting and Data System (BI-RADS) category 4 or 5 lesions and had abnormal mammographic findings in the upper-outer quadrant of the breast were enrolled. Next, MLG was performed. A water-soluble agent was subcutaneously injected into the upper-outer periareolar region of the bilateral breast, and mammography was then performed. Morphologic characteristics, including lymphatic vessel development, the presence of lymphatic vessel defects, and dilation, were recorded for evaluation. RESULTS:Fifty-one patients with BI-RADS category 4 lesions and 40 patients with BI-RADS category 5 lesions were included in the study. Sixty-one patients were found to have malignant disease, whereas 30 patients were found to have benign disease. Morphologic characteristics were recorded for evaluation. The interobserver agreement was evaluated and was classified as excellent according to kappa analysis. The PPV of MLG characteristics for malignant breast disease and lymphatic metastasis was analyzed by logistic regression, and the presentation of a lymphatic vessel defect was the most predictive characteristic of a malignancy (PPV: 0.89; P value: 0.02) in patients with BI-RADS category 4 lesions. Meanwhile, in patients with malignant breast disease, the PPVs for predicting lymphatic metastasis with lymphatic vessel defect and dilation were 0.50 (P value: 0.02) and 0.67 (P value: <0.01), respectively. CONCLUSION:The assessment of morphologic characteristics by MLG has the potential to predict malignant breast disease and lymphatic metastasis.