This study will define a normal range of values for the cross-sectional area (CSA) of the C5-C8 ventral rami in normal subjects and will assess the interexaminer reliability of the CSA measurements. We also describe the normal sonoanatomy of the C5-C8 ventral rami. Thirty-three normal subjects (20 female) were scanned bilaterally. The mean CSA and reference ranges for the C5, C6, C7 and C8 ventral rami were 7.1 +/- 4.1 mm(2), 10.6 +/- 4.3 mm(2), 12.1 +/- 4.1 mm(2) and 10.7 +/- 4.8 mm(2), respectively. The intraclass correlation coefficient (ICC) demonstrated good reliability with a coefficient of 0.76 overall, with individual level coefficients at C5, C6, C7 and C8 of 0.69, 0.71, 0.76 and 0.72, respectively. This is the first study to obtain normative CSA measurements of the C5-C8 ventral rami.