Introduction Focal ulnar nerve compression neuropathy within Guyon's canal in the wrist is an infrequent but debilitating condition often termed Guyon's canal syndrome. Being difficult to diagnose, it has been linked to altered wrist postures, such as in cyclists. The research aim was to determine the effect of wrist angle on ulnar nerve appearance at Guyon's canal utilising high‐resolution sonography. Methods Fifty‐one asymptomatic volunteers underwent a sonographic examination of the ulnar nerve with the wrist held in neutral, 30° flexion and 30° extension. Parameters studied included cross‐sectional area, antero‐posterior diameter, transverse diameter and a flattening ratio of the ulnar nerve. Results The antero‐posterior diameter of the ulnar nerve increases, whilst the transverse diameter decreases with changes in wrist posture from neutral to both flexion and extension. The cross‐sectional area is lower, and the flattening ratio is greater in the neutral compared to non‐neutral wrist positions. Discussion The non‐neutral wrist positions result in deformation of the ulnar nerve within Guyon's canal. The ulnar nerve forms a more cylindrical and less ovoid cross‐sectional shape with changes in wrist angle. Wrists containing accessory muscles overlying Guyon's canal behave in a similar manner.