A dual modality tomosynthesis (DMT) breast scanner has been developed that combines x-ray breast tomosynthesis (XBT) and molecular breast imaging tomosynthesis (MBIT) on a common upright gantry to obtain co-registered structural and functional tomosynthesis images. This paper describes the scanner’s design and operation, and summarizes the results of a pilot clinical evaluation using the tracer 99mTc-sestamibi. The pilot study results suggest that DMT breast scanning is feasible and provides improved specificity and positive predictive value compared to XBT alone. Potential clinical roles for DMT scanning include problem solving for equivocal mammographic/ultrasound studies; as an aid in biopsy target selection following a positive mammogram with multiple suspicious areas; cancer surveillance in patients with a personal history of breast cancer; pre-surgical planning for determination of disease extent; as an alternative for women for whom MRI is impossible; and for monitoring response to neoadjuvant therapy.