Methods: A repeated-measures design was used to evaluate the test–retest reliability of measuring spinal alignment with DEXA. Eighty-six women aged 18–20 years with a diagnosis of IS, who had undergone spinal radiography within the previous 3 months, underwent two DEXA scans (DEXA1 and DEXA2) 1 week apart. Cobb angles were measured on radiographs, DEXA1, and DEXA2 by two independent assessors. Intraclass correlation coefficients (ICCs) were calculated to assess test–retest reliability and inter-rater reliability. Concurrent validity was examined using Pearson’s correlation coefficients between Cobb angles obtained from radiographs and those from DEXA1 and DEXA2 images. Results: Cobb angle measurements from DEXA images had excellent test–retest and nter-rater reliability (ICC>0.90) and very strong concurrent validity with radiographs (r >0.90, p <0.001). The mean difference in Cobb angles between radiographs and DEXA images ranged from 2.37° to 2.91°, whereby the curves were less severe on DEXA images. Conclusions DEXA has consistent reliability and validity for evaluating spinal alignment and is potentially useful in monitoring curve progression in young populations.