OBJECTIVE: Sexual function is an important factor contributing to quality of life. Adult spinal deformity (ASD) patients may have sexual limitations due to lumbar spinal stiffness that may be affected by long-segment fusion. METHODS: This study utilized a multicenter, prospectively defined, consecutive cohort of ASD patients. The primary outcome in this study was the Lumbar Stiffness Disability Index (LSDI) question 10: "Choose the statement that best describes the effect of low back stiffness on your ability to engage in sexual intercourse". RESULTS: In total, 368 patients were included in this study, including 76 men and 292 women, of which 80.7% (n = 293) underwent 9 or more level fusion and 74.4% (n = 270) had pelvic fixation. Baseline LSDI sexual function scores averaged 1.7 (SD 1.3), which improved to 1.3 (SD 1.2) at 2-year follow-up (P = 0.0008). After adjusting for confounding factors, worse LSDI sexual function score was strongly associated with worse Oswestry Disability Index, Scoliosis Research Society-22r total, and SF-36 Physical Component Summary and Mental Component Summary scores at both baseline and 2-year follow-up (p<0.05 for all comparisons). Predictors of poorer baseline sexual function included older age, increased SVA, and increased back pain (p<0.05 for all comparisons). Predictors of improvement in sexual function at 2-year follow-up included sagittal vertical axis improvement (P = 0.0032) and decreased postoperative back pain (P < 0.0001). CONCLUSIONS: This study found that sexual dysfunction scores due to lumbar stiffness significantly improved after surgery for ASD. Additionally, lumbar stiffness-related sexual dysfunction is strongly related to overall outcome measured by Oswestry Disability Index and Scoliosis Research Society-22r total score, highlighting the importance of sexual health on overall outcome in ASD patients.