Summary Flap options for upper limb reconstruction have increased due to better understanding of its vascular anatomy. The posterior interosseus artery flap (PIAF) is used to cover defects of the wrist, hand, proximal thumb, and first web space. This flap has many advantages but requires good knowledge about the anatomy of the posterior interosseus artery (PIOA) and its perforators. Methods Twenty upper extremity cadaveric specimens were injected with red latex, Fine dissection of the PIOA and its perforators took place; the perforators were counted, measured, described and photographed. Twenty patients with dorsal hand defects, had PIAF. Cases have Post-operative care and followed up for 6 months post-operative. Results The PIOA was constant in all cadaveric dissections and gave off 4–8 septocutaneous perforators along its course between the extensor carpi ulnaris (ECU) and extensor digitorum (EDM) muscles. The mean distance of the distal most perforator in the middle third forearm from the ulnar styloid was 10.39 ± 1.54 cm. The anastomosis between the PIOA and the anterior interosseus artery (AIOA) was there in all specimens. Venous congestion occurred in 10% of the cases and was managed conservatively. Necrosis of the distal third of the flap was inevitable in one case; excellent results were obtained in the other cases 90%. Conclusions The posterior interosseus artery flap is an excellent perforator flap for hand reconstruction preserving the ulnar and radial artery; but it has a possible complications such as venous congestion or partial flap necrosis that could be managed conservatively. Level of evidence II.