OBJECTIVE: We determined whether socioeconomic status (SES) and sex are associated with functional status (FS) in axial spondyloarthritis (axSpA). METHODS: We conducted a cohort study of patients with axSpA in the Rheumatology Informatics System for Effectiveness registry. We performed cross-sectional and longitudinal analyses of FS through the Multidimensional Health Assessment Questionnaire (MDHAQ) using generalized estimating equation models. Area Deprivation Index (ADI) was used as an SES proxy. The cross-sectional analysis tested for a linear trend across ADI quintiles for MDHAQ. The longitudinal analysis' outcome was functional decline. We reported predictive margins and assessed for interaction with sex. In the longitudinal analysis, we reported odds of functional decline. RESULTS: In the cross-sectional analysis (N = 5,658), the mean ± SD age was 53.8 ± 15.2 years, 55.8% were female, and 71.4% were non-Hispanic White. The mean ± SD MDHAQ scores were 1.6 ± 2.0 in men versus 2.1 ± 2.2 in women. Predicted mean MDHAQ scores were 2.2 (95% confidence interval [CI] 1.8-2.7) for the lowest ADI quintile and 1.8 (95% CI 1.4-2.1) for the highest. Women had lower FSs compared to men across quintiles. In the longitudinal analysis (n = 2,341), the proportion with FS decline was 14.3% (95% CI 7.6-25.5%) for the lowest SES quintile compared to 9.6% (95% CI 5.2-17.1%) for the highest. Women had 1.7 (95% CI 1.3-2.2) times higher odds of functional decline compared to men. There was no interaction with sex. CONCLUSION: In this large sample of patients with axSpA, those with lower SES had worse FS and functional decline. Women had worse FS than men, initially and over time.