The mammographic features of triple receptor-negative [TRN] breast cancers, a distinct cancer subtype with a poor prognosis have not been reported to our knowledge. The aim of this study was to compare the mammographic breast density, visibility, and tumor features of different breast cancer immunophenotypes. We identified all premenopausal women aged 45 years or less who had been diagnosed with primary breast cancer between January 1999 and November 2005 at a single institution and who had undergone mammography at initial diagnosis. Patient characteristics including clinical, histologic, and mammographic features of breast cancers were tabulated by immunophenotype and compared with the chi-square test or the Kruskal-Wallis test. The P values less than 0.05 were considered statistically significant. We identified 198 premenopausal women who had been diagnosed with breast cancer. Thirty-eight (19%) women had TRN cancer, 67 (34%) had HER2+ cancer, and 93 (47%) had ER+ cancer. Mammographic density and cancer visibility were similar between all immunophenotypes of cancers. TRN cancers were more frequently associated with a mass (33/33 [100%]) than were HER2+ (35/64 [55%]) and ER+ cancers (42/87 [48%]) (P < 0.0001), and were less frequently associated with calcifications (5/33 [15%]) than were HER2+ (43/64 [67%]) and ER+ (53/87 [61%]) cancers (P < 0.0001). Associated ductal carcinoma in situ was reported in 18% (7/38), 57% (38/67), and 48% (52/93) of TRN, HER2+, and ER+ patients, respectively (P = 0.0003). The mammographic features of TRN breast cancer suggest more rapid carcinogenesis leading directly to invasive cancer, that may require adjunct imaging tools for early diagnosis.