Large arm defects remain a challenge to the reconstructive surgeon, as local and regional flaps are limited regarding size and free flaps have disadvantages such as poor color match, technical complexity, prolonged operative time, and the risk of total flap loss. Keystone flaps are fascia-based flaps and combine perforator-based vascularity with relative simplicity of nonmicrosurgical techniques and do not distort local anatomy in cases of malignant excision with wide defects. This article highlights the approach of a multistaged procedure to reconstruct a large arm defect using a keystone type I flap and a temporary synthetic skin substitute for closure in a patient referred to our department for wide resection of a large melanoma in situ on the posterior aspect of the left arm. The defect, measuring 14 cm × 8 cm, was initially reconstructed with a keystone type I flap. Part of the wound was temporarily covered with EpiGARD (Biovision GmbH, Ilmenau, Germany) to avoid excessive wound tension. One week later, the wound was partially narrowed, and a smaller EpiGARD was placed in office under local anesthesia. The multistaged approach was completed with direct closure 1 week later after removal of the smaller EpiGARD. No complications occurred and the result was satisfactory with a pleasing cosmetic result after an 8-month follow-up. In conclusion, the keystone flap allows reconstruction of large arm defects. Temporary synthetic skin substitute coverage can serve as a good addition for those cases where tension on the margins is observed at the price of a small in-office procedure.