PURPOSE In expander based breast reconstruction, providing adequate tissue coverage of the prosthesis is necessary to prevent complications. Placing the expander in a subpectoral pocket may not provide sufficient lateral coverage. Furthermore, inferior release of the pectoralis major to achieve a natural breast ptosis can result in inadequate inferior coverage. In these situations, several muscle, fascial, and allograft options are available for providing adequate expander coverage. The serratus anterior fascia can be used for this purpose but when this fascia is unavailable or inadequate, the subpectoral fascia can be used. This study describes the anatomy of the subpectoral fascia flap, the surgical technique for harvesting it, and an algorithm for choosing between the serratus and subpectoral fascia flaps. Clinical and functional outcomes following use of the subpectoral fascia in expander-based breast reconstruction are reported. METHOD An anatomical study of ten subpectoral fascia flaps was conducted using fresh cadavers to determine the size, vascularity, and anatomical landmarks of the subpectoral fascia flap. Thirteen patients (17 breasts) were included in the study. After approval by the Institutional Review Board, retrospective case note analysis was performed for demographic and perioperative factors. Postoperative complications including capsular contracture, seroma, hematoma, wound dehiscence, and infection were recorded. RESULTS Mean cadaver flap width was 7.0 cm (range: 4.2-15.0 cm) and mean flap length was 13.7 cm (range: 120-190 cm) for a mean surface area of 95.9 cm2. At mean follow-up of 182 days (range 71-276), seroma occurred in one breast, minor wound infection in one breast, and minor wound dehiscence in one breast. There were no incidences of capsular contracture or hematoma. CONCLUSION The subpectoral fascia flap is a novel and safe option for providing vascularized lateral or inferior coverage of prosthesis in expander-based breast reconstruction. Its harvest and use is not associated with adverse clinical outcomes.