[Randomised controlled trials: a reading guide].

This paper, first of a series devoted to evidence-based medicine, describes how to critically read an article on a randomised controlled intervention trial. This guide is applied to the common clinical question, whether or not to prescribe systemic glucocorticoids for patients with exacerbation of chronic obstructive pulmonary disease, through the analysis of two recently published series. It comprises a three-step evaluation: the assessment of the study methods to ensure that the results are valid, the analysis of the results of the larger of the two studies, and the evaluation of whether the results can be applied to a patient whose clinical case illustrates this article. Finally, a few limitations of randomised controlled trials are discussed.