This article discusses the strengths and weaknesses of eight different strategies to measure errors and adverse events. The methods discussed include incident reporting systems, autopsies and morbidity and mortality conferences, malpractice claims, chart review, administrative data analysis, information technology, direct observation, and clinical surveillance. The authors further categorize these measurement strategies based on their relative utility in detecting latent versus active errors as well as adverse events. They also explain how the different methods fit into previously presented and contrasting paradigms (by Leape et al and Shojania et al) for error measurement, patient safety, and evidence-based medicine. This article provides a review and argument for a comprehensive multidimensional approach to measuring errors.