['We describe the methodology for the 2008 update of the Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines. The methodology differs from the 2001 edition in several respects. The most prominent change is the application of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to compiling evidence, assessing the quality of evidence and grading of recommendations.', "Representatives of the GRADE working group joined the ARIA guideline panel to achieve these tasks. While most recommendations result from existing systematic reviews, systematic reviews were not always available and the panel compiled the best available evidence in evidence profiles without conducting actual reviews. The panel conducted two meetings and used the GRADE criteria to assess the quality of evidence (four categories of high, moderate, low and very low) and the strength of recommendation (strong and weak) based on weighing up the desirable and undesirable effects of management strategies, considering values and preferences influencing recommendations, and resource implications. The guideline panel has chosen the words 'we recommend'--for strong recommendations and 'we suggest'--for weak recommendations. Both categories indicate the best course of action for a given patient population, but their implementation, requires different considerations as we describe subsequently in this article."] Do methodology for development of the Allergic Rhinitis and its Impact on Asthma guideline 2008 update?