Orthopedic conditions are common in subjects with Down's syndrome. Few studies have investigated spinal deformities in the frontal and sagittal planes but none have analyzed the pelvic parameters in relation to the spine. The aim was to describe the scoliotic deformities and sagittal spino-pelvic alignment in subjects with Down's syndrome. Forty-one subjects (13 F, 28 M, age 17.4 A 6.2 years) with Down's syndrome, without history of cardiac surgery, had undergone full body biplanar X rays with 3D reconstructions of their spine and pelvis. Subjects were age and gender-matched to 41 asymptomatic subjects (13 F, 28 M, age 17.7 A 5.4 years). Spinal and pelvic parameters were calculated: thoracic kyphosis (TK- T1–T12 and T4–T12), lumbar lordosis (LL- L1–L5 and L1–S1), coronal Cobb angle, axial rotation of the apical vertebra, pelvic incidence (PI), pelvic tilt (PT) and sacral slope (SS). Spino-pelvic parameters were compared between both groups using Student's or Mann-Whitney's tests. Since scoliosis can influence sagittal spinal curvatures, ANCOVA test was used to compare kyphosis and lordosis between groups while eliminating the frontal Cobb angle as a confounding factor. Significance level was set at 0.05. Significant differences on spino-pelvic parameters were found between the Down's syndrome and control group: pelvic incidence (53° vs. 45°, p=0.01), sacral slope (48° vs 37°, p=0.01), pelvic tilt (5° vs 8°, p=0.009), L1–L5 (54° vs 44°, p=0.001), L1–S1 (69° vs 57°, p=0.01), T4–T12 (29° vs 38°, p=0.001), number of patients where the Cobb angle was >10° (20 subjects vs 8 subjects, p=0.005), Cobb angle (11.5° vs 8°, p=0.001), apical vertebral rotation (7° vs 4°, p=0.001). After adjusting for Cobb angle, T1–T12, T4–T12, L1–L5 and L1–S1 remained significantly different between groups (p<0.001 for all parameters). This is the first study that quantifies coronal and sagittal parameters of the spine and pelvis in subjects with Down's syndrome compared to a control group. While in asymptomatic young subjects, a large pelvic incidence and lumbar lordosis are usually associated with large thoracic kyphosis, Down's syndrome subjects presented large pelvic incidence and lumbar lordosis but with low thoracic kyphosis and pelvic tilt. These findings were found to be independent of the degree of scoliotic frontal deformity.