Background: Women with BRCA1/2 or P53 mutations are recommended BC surveillance with mammogram (MMG) and MRI beginning at age 25. The incremental yield of MMG in this age group is not clear. Methods: The MSK Breast Disease Management Team database was queried to identify women diagnosed with BC =< 30 years. Medical records were abstracted to determine clinical characteristics and mode of presentation. Results: Between 1/99 and 7/08, 345 women with BC diagnosed =< 30 years (median 28, 11-30) were evaluated at our institution before definitive treatment. 269 (78%) were white, 23 (6.6%) black, and 13 (3.8%) Hispanic. Most presented with a palpable mass (324/345, 94%) or nipple discharge (9/345, 2.6%). 6 patients (1.8%) were asymptomatic. Median tumor size was 21.5 mm (1-150). Of those with complete information, 147/301 (48.8%) had axillary nodal metastases, 132/345 (44.1%) were HR+ (ER and/or PR+) and HER2-, 76 (25.4%) were TNBC, 33/345 (11%) were HR-/HER2+, and 58/345 (19.4%) were HR+/HER2+. Diagnostic MMG was suspicious for malignancy in 238/286 (83.2%) women. Diagnostic US was abnormal in 307/335 patients (91.6%). Both MMG and MRI were performed before lesion excision in 89 women. MRI demonstrated the lesion of concern in all cases (100%). Additional ipsilateral or contralateral lesions were noted by MRI in 31 women (34.8%). There were 0/89 (0%, 95% CI 0-4%) that were MMG+/MRI-. There were 20/89 cases (22.5%, 95% CI 15-32%) that were MRI+/MMG-. Conclusions: Women diagnosed with breast cancer at or before the age of 30 tend to present with significant local disease. HER2 overexpression appears to be more common than in unselected breast cancer cases. The sensitivity of diagnostic MMG in women with BC =< 30 years is suboptimal, even in a population presenting with palpable masses and relatively large disease. All cancers in this setting were visualized by MRI, and there were no cases where MMG identified MRI-occult BC. Although these women were not undergoing routine screening, these findings suggest that the incremental value of MMG may be limited in women =< 30 who are undergoing MRI-based BC surveillance.