Study Design. Systematic review of clinical guidelines. Objective. To assess the methodological quality of clinical guidelines for the management of acute and chronic low back pain (LBP) in primary care and compare their recommendations. SUMMARY OF BACKGROUND DATA.: A guideline evaluation performed in 2004 concluded that the quality and transparency of the development process and consistency in the reporting of primary care guidelines for LBP need to be improved. At present, several guidelines have been revised and new guidelines are published. We evaluated if the quality of guidelines has improved. Methods. Guidelines published since 2004 were selected by electronically searching in MEDLINE, Cochrane Back Review Group database, Guideline Clearing House, Google, and contacting experts. The methodological quality of the guidelines was assessed by 2 authors independently, using the Appraisal of Guidelines, Research, and Evaluation in Europe instrument. Also, the diagnostic and therapeutic recommendations were compared. Results. Fourteen guidelines were included. In general, the quality was satisfactory. The guidelines had best scores on clarity and presentation. The domain scores of scope and purpose were often moderate due to the absence of description of the clinical questions. The domain of stakeholder involvement scored moderate, mostly because guidelines were not tested among target users. Domains that had generally low scores were applicability and editorial independence. Four guidelines scored low on the rigor of development, but the other guidelines scored high on this domain.The diagnostic and therapeutic recommendations in the guidelines for acute LBP were mainly comparable while the recommendations for the management of chronic LBP varied widely. Conclusion. Compared to the quality assessment performed in 2004, the average quality of guidelines has improved. However, guideline developers should still improve the quality transparency of the development process. Especially the applicability of guidelines and the editorial independence need to be ensured in future guidelines. © 2009, Lippincott Williams & Wilkins.