A cross-sectional study was conducted in 270 Chinese patients with ankylosing spondylitis (AS) in order to identify potential risk factors for severity of spinal structural damage. Two hundred seventy AS patients fulfilled the Modified New York Criteria. Computed tomography (CT) was used to scan sacroiliac and hip joints, and radiography was used to scan anteroposterior and lateral lumbar spine, as well as lateral cervical spine. Bath Ankylosing Spondylitis Radiology Index and modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) were scored in duplicate. One hundred eighty-three patients had low mSASSS (mSASSS, <10), and 87 patients had high mSASSS (mSASSS, ≥10). Univariate analysis revealed that AS age of onset, body mass index (BMI), smoking duration, duration of symptoms, diagnostic delay, hip involvement, and sacroiliitis grade were significantly associated with the risk of having high mSASSS after adjustment (all p's < 0.05). Hip involvement interacted significantly with BMI and smoking duration in a graded manner. Particularly, relative to patients with low BMI-negative hip involvement, those with high BMI-negative hip involvement, low BMI-positive hip involvement, and high BMI-positive hip involvement had a 1.94-fold, 3.29-fold, and 5.07-fold increased risk of high mSASSS (95% confidence interval, 0.84-4.47, 1.37-7.89, and 1.97-13.06, p = 0.118, 0.008, and 0.001, respectively). Finally, a nomogram graph based on 7 significant risk factors was generated with substantial prediction accuracy (concordance index, 0.906). We have identified 7 potential risk factors for the severity of spinal structural damage in Chinese AS patients. Importantly, positive hip involvement, combined with high BMI or long smoking duration, was associated with a remarkably increased risk of having severe spinal structural damage. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.