This study determined the distance between the posterior interosseous nerve and the bicipital tuberosity of the radius in cadavers. Both elbows of 15 preserved cadavers were dissected (eight male cadavers, seven female cadavers). The most prominent point of the radial tuberosity was located, and the shortest distance from this area to the posterior interosseous nerve was measured. The average distance was 2.3 cm (range 1.8 to 3.2 cm); the intracadaver (right vs left) variation was 1.3 mm. The tuberosity to nerve distance was unaffected by forearm rotation. Palpation of the prominence of the radial tuberosity is a reliable guide to the position of the posterior interosseous nerve in dorsal approaches to the proximal forearm.