Objective To develop and validate a patient knowledge questionnaire regarding axial spondyloarthritis (axSpA). Methods Knowledge considered essential for patients with SpA was identified through Delphi rounds among rheumatologists, health care professionals (HPs), and patients, then reformulated to develop the knowledge questionnaire. Cross-sectional validation was performed in 14 rheumatology departments to assess internal validity (Kuder-Richardson coefficient), external validity, acceptability, reproducibility (Lin's concordance correlation coefficient), and sensitivity to change (knowledge score before versus after patient education sessions and effect size). Results SPAKE (SPondyloArthritis Knowledge questionnairE) is a self-administered 42-item questionnaire with a 32-item short-form, both scored 0\textendash 100 assessing knowledge of disease, knowledge of comorbidities, pharmacological treatments, non-pharmacological treatments, self-care, and adaptive skills. In the validation study (130 patients, of whom 67 [51%] were men, mean age 43.5 ± 12.9 years), the mean ± standard deviation score of the long-form questionnaire was 71.6 ± 15.4, with higher scores (better knowledge) in non-pharmacological treatments and adaptive skills and lower scores in cardiovascular comorbidity and pharmacological treatments. Acceptability was good, with no missing data; the internal validity coefficient was 0.85. Reproducibility was good (0.81 [95% CI 0.72\textendash 0.89]). SPAKE showed good sensitivity to change: scores were 69.2 ± 15.3 then 82.7 ± 14.0 (Hedges' effect size: 0.92 [95% CI 0.52\textendash 1.31]). Conclusion SPAKE is a knowledge questionnaire for patients with axSpA, developed with the involvement of HPs and patients and reflecting current recommendations for the management of axSpA. SPAKE will be useful in assessing knowledge acquisition and self-management strategies in routine care and research.