Objective To evaluate and compare spiral CT and positron emission tomography-CT (PET-CT) in characterization of of axillary lymph nodes in breast cancer patients.Methods Forty patients with pathologically proven breast Cancer underwent contrast-enhanced spiral CT of tbe breast and axilla,13 of them also underwent PET-CT examination.One hundred and fifty-eight axillary lymph nodes were found in the 40 patients through contrast enhanced spiral CT,while 57 lymph nodes were found in the 13 patients through PET-CT.Three radiologists rated the lymph nodes found in CT images on a five-point scale.If the score was equal to or greater than 3,it was defined as positive (metastatic),otherwise negative.Visual observation and semiquantitative analysis were used to classify lymph nodes in PET-CT images.The results of spiral CT observation and PET-CT observation of lymph nodes were compared with pathological results.The relative value of CT and PET-CT was analyzed.Exact probability statistics were employed.Results One hundred and fifty eight lymph nodes of 40 patients were detected by spiral CT,91 of them were diagnosed as positive and 67 as negative Among the lymph nodes found in spiral CT,99 were positive and 59 were negative pathologicall.A total of 57 lymph nodes were found by PET-CT.Thirty-nine of them were defined as positive and 18 as negative.Among the lymph nodes found in PET-CT,39 were positive and 18 were negative pathologically.The sensitivity,specificity,accuracy,positive and negative predictive values in CT prediction in axillary lymph nodes metastases were 88.89%,94.91%,91.14%,96.70%,and 83.58%,respectively.The sensitivity,specificity,accuracy,positive and negative predictive values in PET-CT prediction in axillary lymph nodes metastases were 97.44%,94.44%,96.49%,97.44%,and 94.44%,respectively.PET-CT had no significant difference with spiral CT in sensitivity,accuracy,positive and negative predictive values for detection of axillary lymph nodes in breast cancer.But there was significant difierence between PET-CT and CT in negative predictive value(P＜0.05).Conclusions Both helical CT and PET-CT were the efficient methods in predicting the axillary lymph node status in breast cancer patiens.The negative predictive value of PET-CT was higher than that of helical CT.PET-CT has a better predictive ability than CT for the presurgical evaluation for breast cancer patients.