Aim: High-resolution ultrasonography is a new and promising technique to evaluate peripheral and spinal nerves. Its validity as a diagnostic tool in neurological diseases has been demonstrated in adults. The aims of study were to establish the reference values for the cross-sectional area of the normal sciatic nerve on high-resolution ultrasonography, and to determine the relationship between the cross-sectional area of the normal sciatic nerve and the subjects’ age, gender, height (in cm), weight (in kg), and body mass index. Material and methods: Two hundred subjects of both genders and above 18 years of age were studied with high-resolution ultrasonography. The subjects had no history of peripheral neuropathy or trauma to the lower limb. The cross-sectional areas of the normal sciatic nerves were obtained at two different levels in both lower limbs. The mean cross-sectional areas of the sciatic nerves were measured at two different levels, one located at 1 cm above the bifurcation of the sciatic nerve into the tibial and common peroneal nerves, and the other 4 cm above the bifurcation of the sciatic nerve into the tibial and common peroneal nerves. Results: A positive correlation of the mean cross-sectional area was established with height, weight, and body mass index. Women had smaller cross-sectional areas of the normal sciatic nerves than men at both measuring sites. No significant relationship was established with the age of the subjects. Conclusions: The established reference values of the cross-sectional area of the sciatic nerve can facilitate the analysis of pathological nerve conditions.