Objectives: Chronic low back pain (CLBP) is a common health problem and in most patients it is not possible to identify a specific cause (non-specific CLBP). Spondyloarthritis is a musculoskeletal disorder characterized by (often inflammatory) back pain and spinal stiffness. The impact of CLBP and spondyloarthritis on patients’ physical function may be different. This study aims to compare physical disability in patients with spondyloarthritis and CLBP, in a population-based setting. Furthermore, we aim to identify modifiable risk factors for physical disability among these two populations. Methods: Data from EpiReumaPt, a national health cohort with 10 661 individuals, conducted from September 2011 to December 2013, was used. Physical function was accessed by the Health Assessment Questionnaire Disability Index (HAQ-DI) and by the physical function dimension of the 36-Item Short Form Survey (SF-36). Univariable and multivariable linear regression analyses were used to assess the differences between groups. Factors associated with physical disability were explored for both diseases. Results: We evaluated 92 patients with spondyloarthritis, 1376 patients with CLBP and 679 subjects without rheumatic and musculoskeletal diseases (RMDs). Spondyloarthritis and CLBP patients reported significantly higher levels of disability in HAQ-DI (ß=0.33; p < 0.001 and ß=0.20; p < 0.001, respectively) than subjects without RMDs. In comparison to CLBP patients, spondyloarthritis patients reported higher disability (ß=0.14; p=0.03). The physical domains of SF-36, bodily pain and general health, where more affected in spondyloarthritis patients than in CLBP patients (ß=-6.61; p=0.02 and ß=-5.94; p=0.001, respectively). Spondyloarthritis and CLBP patients had a worse physical summary score (PCS) than mental summary score (MCS), and only PCS was significantly worse in comparison to subjects without RMDs. Factors associated with physical disability in CLBP were low back pain intensity, older age, obesity, multimorbidity, and retirement. Similarly, in spondyloarthritis physical disability was associated with retirement and multimorbidity. Factors associated with lower disability were alcohol consumption and male gender in CLBP, and regular physical exercise was associated with lower disability in both disorders. Conclusions: In this nationwide cohort, spondyloarthritis and CLBP patients reported significant physical disability. Regular physical exercise was associated with lower disability in both diseases.