Objective: To determine if differentiation of pure and mixed mucinous carcinoma is possible by correlating the mammographic and ultrasonographic appearances with the histologic features. Materials and methods: We retrospectively reviewed the pathology reports of 406 women with diagnosis of breast carcinoma between January 1997 and October 1999 and found that 10 (2.5%) had mucinous carcinoma. Four patients without mammography and ultrasonography were excluded. The remaining 6 patients (age range 40-68 years; mean 47.8 years) were the subjects of the study. Results: All 6 patients had palpable breast masses. The breasts were heterogeneously dense in 4 patients, homogeneously dense in one case and scattered fibroglandular in one case. Histopathologic review showed 5 pure mucinous tumors and one mixed mucinous tumor. The tumor diameter ranged from 1.2 to 2.8 cm (mean 2.16 cm). The mammographic findings in the pure tumor group consisted of well defined, lobulated solitary masses in 4 cases and a poorly defined solitary mass in one patient who had a very dense breast. Mammogram in one patient with mixed mucinous carcinoma showed an area of focal increased density. All tumors showed no calcification. Ultrasonographic findings in the pure tumor group included well-defined homogeneous hypoechoic mass in 2, well-defined isoechoic mass in 2 and well-defined inhomogeneous echoic mass in one case. Ultrasonographic findings in a patient with mixed mucinous carcinoma was an irregular isoechoic mass. No metastasis was found in the axillary lymph nodes in both pure and mixed mucinous carcinomas. Conclusion: Mammographic and ultrasonographic appearances of pure and mixed mucinous tumors are different. A well-defined tumor is characteristic of pure mucinous tumor while an irregular tumor may be characteristic of mixed mucinous tumor.