Lateral whole-spine radiography is a useful tool in the management of spinal deformity, but the most appropriate arm position during radiography has yet to be determined. In this prospective study, we evaluated 26 adult volunteers and 22 patients with lumbar spinal canal stenosis. Lateral whole-spine radiographs were acquired in the most stable and relaxed position while the subjects were standing with their arms extended and their hand gently clasped in front of the trunk (clasped position). The following parameters were measured: sagittal vertical axis (SVA), lumbar lordotic angle (LLA), pelvic angle (PA), pelvic lordosis angle (PRS1), pelvic tilt (PT), and pelvic incidence (PI). The reliability of measurements was assessed by interclass correlation coefficients. The SVA was slightly positive in volunteers. LLA, PA, PRS1, PT, and PI were compatible with standard normal values. The results showed "almost perfect agreement" with regard to intra- and interobserver reliability. The clasped position can be used effectively and reliably for measurement of sagittal spinal alignment for the lumbar region in adults.