Methods: Data from 12 adults without any history of back pain were used in this study. Sagittal T2-weighted images of the lumbar spine were acquired in the supine and WB positions twice (in two separate sessions scheduled within a week). Linear, angular dimensions, and cross-sectional areas (CSAs) were measured using proprietary software. Supine and WB data acquired from the two imaging sessions were tested for intra-rater reliability. Quantified data were normalized for each session to test the significance of differences. ICC was calculated to test the reliability of the measurements. Results: Linear, angular, and CSA measurements demonstrated strong within-position (supine and WB) correlations (r -values, 0.75–0.97). Between-position (supine vs. WB) differences were significant for all measured dimensions (p<0.05). Between-session measurements demonstrated a strong correlation (r -values, 0.64–0.83). Calculated ICC showed strong agreement among the measurements. Conclusions Anatomical dimensions of the lumbar spine may demonstrate consistent and significant differences between supine and WB MRI for specific structural parameters.