Background Despite the increasing number of manuals on how to develop clinical practice guidelines (CPGs) there remain concerns about their quality. The aim of this study was to review the quality of CPGs across a wide range of healthcare topics published since 1980.

Methods The authors conducted a literature search in MEDLINE to identify publications assessing the quality of CPGs with the Appraisal of Guidelines, Research and Evaluation (AGREE) instrument. For the included guidelines in each study, the authors gathered data about the year of publication, institution, country, healthcare topic, AGREE score per domain and overall assessment.

Results In total, 42 reviews were selected, including a total of 626 guidelines, published between 1980 and 2007, with a median of 25 CPGs. The mean scores were acceptable for the domain ‘Scope and purpose’ (64%; 95% CI 61.9 to 66.4) and ‘Clarity and presentation’ (60%; 95% CI 57.9 to 61.9), moderate for domain ‘Rigour of development’ (43%; 95% CI 41.0 to 45.2), and low for the other domains (‘Stakeholder involvement’ 35%; 95% CI 33.9 to 37.5, ‘Editorial independence’ 30%; 95% CI 27.9 to 32.3, and ‘Applicability’ 22%; 95% CI 20.4 to 23.9). From those guidelines that included an overall assessment, 62% (168/270) were recommended or recommended with provisos. There was a significant improvement over time for all domains, except for ‘Editorial independence.’

Conclusions This review shows that despite some increase in quality of CPGs over time, the quality scores as measured with the AGREE Instrument have remained moderate to low over the last two decades. This finding urges guideline developers to continue improving the quality of their products. International collaboration could help increasing the efficiency of the process.