OBJECTIVE To evaluate the role of sonography in evaluation of abnormal axillary lymph nodes identified in patients with otherwise negative or benign findings on mammography. METHODS For 3 years 2 months, we retrospectively reviewed 30 consecutive cases that had undergone sonographic evaluation for abnormal axillary lymph nodes identified in patients whose mammograms had an American College of Radiology Breast Imaging Reporting and Data System final assessment of 1 or 2. Mammographic and sonographic features of the lymph nodes were analyzed and correlated with the histologic diagnosis in patients undergoing biopsy. Patients who did not undergo biopsy had clinical or imaging follow-up. RESULTS Twenty of the 30 patients studied had an abnormal sonographic appearance. Biopsy was recommended in 17 of the 20 patients on the basis of an abnormal sonographic appearance. In the remaining 3 patients, there was an underlying cause for lymphadenopathy, and these patients underwent clinical and sonographic follow-up. Eighteen patients underwent biopsy, including 1 patient with normal findings on sonography. Ten of these patients had malignant histologic findings: 6 were metastatic adenocarcinoma; 1, poorly differentiated sarcoma, and 3, lymphoma. The remaining 8 patients had benign histologic findings. The nonbiopsy group had clinical and or imaging follow-up (mean, 17.6 months; range, 6-25 months). The sensitivity (true-positive/true-positive + false-negative) of sonography for assessment of suspected abnormal lymph nodes in the patients studied was 100% (10 of 10); specificity (true-negative/true-negative + false-positive), 50% (10 of 20); positive predictive value (true-positive/true-positive + false-positive) for malignancy based on the presence of 2 or more abnormal sonographic features, 50% (10 of 20); and negative predictive value, 100%. CONCLUSIONS Sonography is useful in further characterization of isolated abnormal axillary lymph nodes identified on mammography. Sonographic evaluation helps improve the specificity of imaging evaluation in assessment of these lymph nodes.