AbstractA method for measuring the cross‐sectional area (CS area) of the peroneal nerve muscle groups (PNMG) by ultrasonography is presented. The method has a good reliability and can be performed easily. The mean value of the ratio (× 100) of the right‐sided PNMG CS area to the left‐sided PNMG CS area in right‐handed normal subjects was 98%, with a standard deviation of 8.5%. The normal range for this value was 81%−115% (mean ± 2 SD). Examples of these measurements in patients with peroneal pareses during denervation and reinnervatio