The reports of transfer of the medial arm flap have been inconsistent, and confusion remains about its anatomy and use. The advantages of this donor site, however, justify new researches about the vascular anatomy of the flap. In this study, the vascular supply to the medial side of the arm was analysed in fifteen fresh cadaver dissections. The methods, the anatomical bases, and the technique of elevation of the flap were detailed. Methylene blue injection studies showed the extent of the medial arm flap. The authors found that, in most cases, the superior ulnar collateral artery was the main vessel of this flap, giving cutaneous branches to medial arm skin. The diameter of the superior ulnar collateral artery was measured and considered adequate for microsurgical transfer. If no major cutaneous branches are noted from superior ulnar collateral artery, then a significant direct cutaneous branch from the brachial artery will be always present. With this in mind, the dissection must initially proceed carefully, preserving all vessels that may contribute to cutaneous perfusion. The authors conclude that with knowledge of its anatomical variations, the medial arm flap is a plausible reconstructive option.