A unique case of cystic hypersecretory carcinoma in a 48-year-old woman who presented with a tender, palpable abnormality of the lower outer quadrant of her left breast in 2002 is described. Mammographic and ultrasound examinations showed heterogeneous, dense breast tissue with a focal asymmetric density and an ill-defined heterogenous hypoechoic area with anechoic spaces, respectively, that corresponded to the area of palpable abnormality. Although the imaging findings did not change significantly over 4 years, the patient complained of intermittent, spontaneous serous discharge from the left nipple and persistent induration and tenderness in the same area of the left breast. An ultrasound-guided core-needle biopsy of the lesion was performed at the last visit to rule out a malignant process. A left simple mastectomy showed a large multicystic lesion occupying most of the lower quadrants by a cystic hypersecretory carcinoma and Paget disease of the nipple. © 2008 Sage Publications.