Guidelines for the diagnosis and management of asthma have been available for the past 13 years and are updated regularly. However, asthma guidelines are rarely completely up-to-date because our knowledge about the pathophysiology and treatment of asthma is continually evolving. Guidelines are an increasingly familiar part of clinical practice and may have potential benefits and harms. The potential harms of guidelines can be minimized if they are rigorously developed using evidence-based medicine. Guidelines should identify key decisions and their consequences and should review the consequences of alternative decisions. In addition, guidelines should be simple, user-friendly and widely disseminated. Guidelines evolve over time and their recommendations should be supported by evidence from clinical trials. Evidence-based medicine is the new paradigm but the results and reaction to the recent meta-analysis on house-dust mite control measures highlights the need for care when incorporating such information into guidelines. Newer therapeutic agents such as the leukotriene receptor antagonists are included in the most recent revision of the GINA guidelines, but their position in asthma therapy is not yet fully established. In countries where asthma guidelines have been implemented, there appears to have been a reduction in the prevalence of moderate persistent asthma but no decrease in severe asthma. This indicates that there is still room for improvement.