To define the anatomical relationships of the nerves to the common arthroscopy portals at the elbow an arthroscope was introduced into 20 cadaver elbows and the positions of the nerves were then determined by dissection. In all cases the posterior interosseous nerve lay close to the radiohumeral joint and to the anterolateral portal. Pronation of the forearm displaced the nerve away from the arthroscope. The median nerve passed consistently within 14 mm of the arthroscope when it was introduced through the anteromedial portal. The branches supplying the superficial forearm flexor muscles were at risk.