Thirty upper limbs from skeletally mature embalmed cadavers were studied to define the most common pattern of the terminal branches of the posterior interosseous nerve. At 0.43 +/- 0.52 cm from the distal edge of the superficial head of the supinator and 8 +/- 1.6 cm from the lateral epicondyle, the posterior interosseous nerve branches, forming a common leash. There were six branches, which were arranged from the ulnar to the radial side at their origin from the common leash. The first and second branches supplied the extensor digitorum communis, the third branch supplied the extensor carpi ulnaris, the fourth branch supplied the extensor digiti minimi, and the fifth branch arose from the undersurface of the common leash and divided into two branches (medial and lateral) at 10.1 +/- 3.2 cm distal to the lateral epicondyle and 12.8 +/- 2.2 cm proximal to Lister's tubercle. The medial branch supplied the extensor pollicis longus and extensor indicis proprius. The lateral branch supplied the extensor pollicis longus and extensor pollicis brevis and ended at the wrist capsule. The sixth branch arose from the radial side of the common leash and divided into three branches. The first branch supplied the abductor pollicis longus and extensor pollicis brevis. The second branch supplied the abductor pollicis longus. The third branch supplied the superficial head of the supinator. The authors of this study describe the most efficient way to identify the six branches and how to avoid the risk of damaging them during surgical exposure.