Introduction The aims of this study were to identify factors affecting the measurement of nerve cross‐sectional area (CSA) and to establish normal reference values for nerve ultrasonography of the upper extremity. Methods Ninety‐seven age‐matched, healthy individuals were enrolled. Ultrasonographic tests were performed by tracing nerves from the axilla to the distal arm. CSA was measured at the following locations: median nerve (carpal tunnel inlet, forearm, antecubital fossa, midhumerus); ulnar nerve (wrist, 2 cm proximal to the wrist, forearm, cubital tunnel outlet and inlet, midhumerus); radial nerve (spiral groove, antecubital fossa); and musculocutaneous nerve (proximal humerus). Results The CSA reference values differed between the measured points along the path of each nerve. Nerve CSA correlated significantly with weight, body mass index, height, and gender; however, the CSA ratio (distal/proximal) did not correlate with demographic factors. Conclusions The normal reference values may be helpful in diagnosis of pathologies involving these nerves. Muscle Nerve 47: 864–871, 2013