Background: Dense breasts increase a woman's risk of developing cancer while also raising the likelihood of a missed diagnosis from traditional mammography screening. Digital Breast Tomosynthesis (DBT) has been shown to identify positive breast cancer more accurately in women with dense breasts, but no study has estimated the cost-effectiveness of this screening mode under a notification requirement. Methods: Taking the perspective of a healthcare system, we estimated the incremental cost-effectiveness ratio (ICER) of providing DBT as an alternative to mammography for 40-year old women. Model parameters reflecting risk of breast cancer, detection rates, and costs were estimated from recent meta analyses, Tufts’ CEA registry, and Medicare Fee Schedules. We used probabilistic Markov Models to estimate the ICER under uncertainty, and a time-variant model in which breast density and cancer risk change over time. Additionally, a heterogeneity analysis included all women between the ages of 40-65, while also using 1^st and 2^nd degree family history to calculate cancer risk. Results: In the probabilistic model, adjunctive DBT has a cost differential of $12,203, with an increase of 0.0382 quality-adjusted life years (ICER = $319,491/QALY) compared to mammography. This result was most sensitive to the probability of a missed diagnosis for women with dense breasts. At a willing-ness to pay of $50,000, adjunctive DBT had a 57% chance of being more costly and less effective than standard mammography. Conversely, DBT only had a 20% chance of being cost-effective and a 9.9% chance of being less costly and more effective. The time-variant model reported an ICER of $174,218, but adjunctive DBT became even more cost-effective after expanding the population and including family history of cancer (ICER_All Ages = $157,146; ICER_FamHist = $153,388). Conclusions: Breast density notification laws which provide additional screening via DBT are not cost-effective at a willingness to pay of $50,000. Policymakers, however, should note that many modern cancer therapeutics also exceed this threshold. As an adjunctive screening technique, DBT would result in fewer deaths and increase quality of life, but the effect is minimal and carries a high cost. Including breast density within greater risk stratification protocols, however, may prove highly cost-effective, especially for older women with a family history of cancer.