STUDY DESIGN: Cross-cultural adaptation and cross-sectional psychometric testing. OBJECTIVES: To translate and culturally adapt the Moroccan version of the Roland Morris Disability Questionnaire and to validate its use for assessing disability in Moroccan patients with low back pain (LBP). SUMMARY OF BACKGROUND DATA: The RMDQ is a reliable evaluation instrument for LBP disability, but no validated Moroccan version is available. METHODS: The RMDQ was translated and back-translated to dialectal Arabic, pretested, and reviewed by a committee following the Guillemin criteriIt was then validated on 76 Moroccan patients with chronic LBP. Reliability for the 1-week test-retest was assessed using internal consistency by Cronbach's alpha coefficient, the intraclass correlation coefficient, and the constructed Bland Altman plot. Structure validity was evaluated by multiple correspondence analysis. External construct validity was assessed by association with pain, spinal mobility, and other key variables (weight, height, duration of LBP). RESULTS: The reproducibility of the 24 items was satisfactory with a kappa statistic of agreement superior to 0.6 except item 10 and ranging from 0.47 to 0.9. The intraclass correlation coefficient for global score reproducibility was good and reached 0.93 (95% confidence interval, 0.89-0.95). The constructed Bland and Altman plot for test-retest agreement showed a good reliability. The internal consistency was very good with a Cronbach's alpha coefficient of 0.96. The multiple correspondence analysis for internal structure validity showed a preponderant factor explaining 22% of the variance in the score. The construct validity showed a positive correlation between RMDQ and the visual analog scale (r = 0.32; P = 0.005). There was no statistic correlation between RMDQ and the other variables. CONCLUSION: The Moroccan version of the RMDQ has good comprehensibility internal consistency, reliability, and validity for the evaluation of Moroccan-speaking patients with LBP.