||STRUCTURED ABSTRACT: Study Design. Multicenter, prospective, consecutive case series.Objectives. To assess prevalence and type of cervical deformity among adults with thoracolumbar (TL) deformity and to assess for associations between cervical deformities and different types of TL deformities.Summary of Background Data. Cervical deformity can present concomitantly with TL deformity and have implications for the management of TL deformity.Methods. Multicenter, prospective, consecutive series of adult (age>18) TL deformity patients. Parameters included pelvic tilt (PT), pelvic incidence (PI), lumbar lordosis (LL), C2-C7 sagittal vertical axis (C2-C7SVA), C7-S1SVA and C2-C7 lordosis (CL). Cervical deformity was defined as CL>0° (cervical kyphosis [CK]) or C2-C7SVA>4cm (cervical positive sagittal malalignment [CPSM]). Patients were stratified by the SRS-Schwab TL deformity classification, including curve type (N = sagittal deformity, T = thoracic scoliosis, L = lumbar scoliosis, D = T+L scoliosis) and modifier grades: PT (0:<20°, +:20-30°, ++:>30°), C7-S1SVA (0:<4cm, +:4-9.5cm, ++:>9.5cm), PI-LL mismatch (0:<10°, +:10-20°, ++:>20°).Results. 470 patients met criteria (mean age = 52yrs). Mean CL and C2-C7SVA were -8° and 3.2cm, respectively. CK and CPSM prevalence were 31% and 29%, respectively, and prevalence of CK and/or CPSM was 53%. CK prevalence differed by curve type (N = 15%, L = 27%, D = 37%, T = 49%; p<0.001); CPSM prevalence did not differ by curve type (p = 0.19). Higher PT grades had lower CK prevalence (0 = 40%, + = 27%, ++ = 15%; p<0.001) but greater CPSM prevalence (0 = 23%, + = 28%, ++ = 45%; p = 0.001). Similarly, higher SVA grades had lower CK prevalence (0 = 40%, + = 23%, ++ = 11%; p<0.001) but greater CPSM prevalence (0 = 24%, + = 24%, ++ = 48%; p<0.001). Higher PI-LL grades had lower CK prevalence (0 = 35%, + = 31%, ++ = 22%; p = 0.034) but no CPSM association (p = 0.46).Conclusions. Cervical deformity is highly prevalent (53%) in adult TL deformity. C7-S1SVA, PT, and PI-LL modifiers are associated with cervical deformity prevalence. These findings suggest that TL deformity evaluation should include assessment for concomitant cervical deformity and that further study is warranted to define their potential clinical impact.