The functional anatomy of the interosseous membrane (IOM) of the forearm was studied in 15 fresh frozen cadavers. The IOM consisted of three components: the tendinous part; the membranous part; and the dorsal oblique accessory cord. The tendinous part was a thick and strong complex of three to ten bundles which run from the proximal one third of the radius to the distal quarter of the ulna. The membranous part was recognised as a soft and thin structure, adjacent proximal and distal to the tendinous part. The dorsal oblique cord was found as a single cord on the dorsal side of the IOM from the proximal quarter of the ulna to the middle region of the radius. This cord was distinct from the oblique cord, which existed on the palmar side of the forearm separated from the IOM. The IOM was flat in the neutral position, while it flexed along the rotation axis in pronation and supination. Since the prominence of the curvature in the IOM was almost in the same direction as the fibres of the tendinous part, the tendinous part demonstrated only bending, similar to partial bending of an elastic board. The bending position was changed with the forearm position and the tightened bundles in the tendinous part were altered during rotation.