OBJECTIVE Although uncommon, breast cancer is the leading cause of cancer death in young women. There are limited studies on the presentation and characteristics of breast cancer in women under age 40. METHODS This is a retrospective study investigating patient demographics, clinical presentations, imaging findings, and cancer characteristics of a cohort of 145 women under age 40 with breast cancer. RESULTS Our cohort had more aggressive cancer subtypes than reported in older women; 33.1% triple negative, 80% high Ki-67, and 21.3% with stage 3+ disease. Most were referred from primary care or obstetrician/gynecologist, though 5.5% initially presented from the emergency department and another 2.1% were incidental findings. 16.6% of patients presented while pregnant or breastfeeding. Most patients presented with breast related symptoms. Of the 9.1% of patients diagnosed through our high-risk screening program, 84.6% of the cancers were identified on mammography or simultaneously with mammography and MRI. Most breast cancers presented with typically worrisome imaging (82.6%), though several cancers presented with findings that were typically benign. CONCLUSIONS We recommend prompt breast imaging for young women presenting with breast-related symptoms or an incidental breast finding, as younger patients have more aggressive cancer subtypes and are of a higher grade at presentation compared to older women. We also recommend vigilance when distinguishing suspicious symptoms from pregnancy-related breast changes to minimize delays in diagnosis. Additionally, it is important to identify patients who qualify for high risk screening, since cancers in screening patients were found at a lower grade than those presenting with symptoms.