This study was conducted to evaluate the capability of ultrasonography to visualize extremity nerves. Fifty healthy women and men and 10 patients suffering with hereditary motor and sensory neuropathy (HMSN) were examined. The radial nerve lateral to the humerus, ulnar nerve distal to the cubital tunnel, median nerve in the middle of the forearm and proximal to the palmar crease, sciatic nerve in the middle of the thigh and tibial and common peroneal nerves just distal to their bifurcation, were investigated, employing a 7.5-MHz electronic linear-array transducer. In healthy subjects, the median, ulnar and radial nerves could be identified in all cases, the sciatic nerve in 37 cases, the tibial and peroneal nerves in 10 cases. The median values of thicknesses were about 3 mm for arm nerves and 6 to 7 mm for the sciatic nerve. Nerve sizes did not correlate with subjects' height, weight or age. In the majority of the patients, arm and sciatic nerves were also visible. Thicknesses were normal in 34, increased in 11 and decreased in six of 51 nerves. In conclusion, ultrasonography allows reliable imaging of the major arm nerves and, occasionally, facilitates visualization of the sciatic, tibial and peroneal nerves in healthy subjects. Nerve size and structure did not differ significantly between patients with HMSN and healthy subjects.