The purpose of this review is to present a guide to help readers critically appraise the methodologic quality of an article or articles describing a clinical decision rule. This guide will also be useful to clinical researchers who wish to answer 1 or more questions detailed in this article. We consider the 6 major stages in the development and testing of a new clinical decision rule and discuss a number of standards within each stage. We use examples from emergency medicine and, in particular, examples from our own research on clinical decisions rules for radiography in trauma. [Stiell IG, Wells GA: Methodologic standards for the development of clinical decision rules in emergency medicine. Ann Emerg Med April 1999;33:437-447.]