We live in an era when medical practice is increasingly regulated by guidelines and protocols. Ideally, such guidance should be evidence based, and in particular it is generally recommended that advice on medical treatment should be based on the results of adequately powered, double blind, placebo controlled trials or, some would say, better still, a meta-analysis of several such trials. Unfortunately, evidence of this standard is often lacking, and many guidelines amount to little more than the opinions of the authors. This is not to say that opinion based guidelines are valueless—the opinions of experienced clinicians may be better than no opinion at all. Thus, a significant proportion of the advice contained in the first edition of the British Thoracic Society Guidelines on asthma management1 was opinion, rather than evidence based, yet its publication was followed by a fall in childhood asthma admissions. This fall might have reflected some unknown benign environmental influence, but was much more likely to have resulted from improved management of asthma in the community as the guidelines gradually changed clinical practice. Moreover, guidelines that indicate areas where supporting evidence is lacking can point the way to future research. The publication of the asthma guidelines was followed by various papers presenting evidence that had hitherto been lacking, for instance in relation to the use of intravenous aminophylline in acute asthma.2 This month sees the publication in our sister journal Thorax of a new set of Guidelines,3 this time on the management of community acquired pneumonia in children. In preparing these Guidelines, the authors have followed a well trodden path. An extensive literature review was followed by close scrutiny of apparently relevant papers. Those of us who have sat on guideline working parties will appreciate how this process, which can involve the review …