The present study was undertaken to determine the relationship between spinal radiological changes of ankylosing spondylitis (AS), spinal mobility, and physical functioning. Thirty-one patients diagnosed as AS according to the modified New York criteria for AS were included in this study. Three radiographic scoring methods were used to assess spinal damage. Severity of spinal involvement was assessed by using Stoke Ankylosing Spondylitis Spine Score (SASSS) and Bath Ankylosing Spondylitis Radiographic Index–Spine (BASRI–S). To assess the extent of spinal involvement, the total number of vertebrae showing radiological findings attributable to AS [number of vertebrae involved (NoVI)] was calculated according to the AS grading system defined by Braun et al. Statistical analysis, consisting of bivariate correlation, Spearman correlation, and multiple linear regression analysis, was performed using Windows Statistical Package for the Social Sciences 13.0. NoVI was negatively correlated with modified Schober and lateral spinal flexion and was positively correlated with occiput-to-wall distance and BASMI. SASSS was negatively correlated with the modified Schober. BASRI–S was negatively correlated with the modified Schober and positively correlated with BASMI. When BASMI and Bath Ankylosing Spondylitis Functional Index were taken as dependent variables, only the NoVI was found to be associated with BASMI. In our data, the extent of spinal involvement (NoVI) showed a more significant correlation with spinal measurements such as modified Schober and BASMI as compared with the other radiologic scores (SASSS and BASRI–S). Furthermore, because only the NoVI was found to be associated with BASMI, we can conclude that the extent of spinal involvement, which also includes thoracic vertebrae, affects spinal measurements.