PURPOSE: To evaluate the clinical and imaging findings of signet ring cell carcinoma of the breast. MATERIALS AND METHODS: We retrospectively evaluated the clinical, mammographic and ultrasonographic (US)findings of five patients aged 23 -49 (mean 37) years with signet ring cell carcinoma of the breast. Diagnosis involved US-guided core-needle biopsy. In all patients the stomach was evaluated endoscopically after confirmation of the breast lesion. Metastatic breast cancer was confirmed in four patients and primary breast cancer in one. RESULTS: Three of the four patients with metastatic signet ring cell carcinoma complained of breast pain and swelling or enlargement. Mammography indicated the presence showed of diffuse increased density and skin thickening, without calcifications, while US demonstrated diffuse marked skin thickening, lymphatic dilatation, and axillary lymph node enlargement. Neither modality revealed the presence of mass, however. In the remaining patient, an enlarged breast mass was observed; mammography showed no abnormality, but US revealed an illdefined hypoechoic mass. Mammographic and US findings in the patient with primary signet ring cell carcinoma of the breast indicated an ill-defined spiculated mass, resembling other breast carcinomas. CONCLUSION: Metastatic signet ring cell carcinoma of the breast showed clinical symptoms similar to these seen in inflammatory breast cancer, though the former condition occurred in younger women. Radiographs demonstrated diffuse increased density and skin thickening without associated microcalcifications or mass.