In breast cancer patients, the number of surgically resected metastatic axillary lymph nodes has been considered to correlate closely with patient prognosis. Therefore, if metastatic lymph nodes could be controlled by neoadjuvant chemotherapy pre-operatively, we would be able to select a more appropriate regimen of post-operative chemotherapy for the individual patient and expect prognostic advantages of each patient with node-positive breast cancer. In this study, we aimed to evaluate the therapeutic effect of neoadjuvant chemotherapy for metastatic lymph nodes of node-positive breast cancer patients, using thin-section (5 mm) helical CT (prone-position) with bolus injection of contrast agent. Between April 1994 and March 2002, 49 patients with node-positive breast cancer who had undergone thin-section CT study both before and following neoadjuvant chemotherapy enrolled in the study. The mean age of the patients was 48.9 years and all were female. Concerning metastatic lymph nodes status, 45 patients were classified as N1, 2 patients as N2, and another 2 as N3. In the evaluation, if at least one lymph node of >5 mm in the short diameter was detected on the CT study, the case was classified as node-positive. For lymph nodes of >1 cm in short diameter, fine-needle aspiration biopsy guided by ultrasonography was performed in order to obtain pathological confirmation of the existence of cancer metastasis. The diagnostic results of the CT study were compared with the pathologic findings of the resected specimen operatively. The neoadjuvant chemotherapy consisted of 3 to 4 times of CAF chemotherapy and an anti-estrogen agent, and intra-arterial infusion chemotherapy was also performed in patients with lymph node status of N2 or N3. The axillary status of 15 (30.6%) out of the 49 patients was evaluated as N0 after neoadjuvant chemotherapy, and 14 out of the 15 patients were confirmed as node-negative based on the pathological results. Therefore, the diagnostic accuracy of the second CT study performed following the neoadjuvant chemotherapy was 85.7%, with a sensitivity of 96.6%, a specificity of 70.0%, a positive predictive value of 82.4%, and a negative predictive value of 93.3%. The results described above demonstrate that such a sophisticated and precise CT study performed following neoadjuvant chemotherapy and evaluating the therapeutic effect on metastatic lymph nodes following the neoadjuvant chemotherapy can help to determine an appropriate regimen of post-operative chemotherapy and be of prognostic advantage in patients with node-positive breast cancer.