Since the publication of a paper by the American Society of Hypertension, Inc. Writing Group in 2003, some refinements have occurred in the definition of hypertension. Blood pressure is now recognized as a biomarker for hypertension, and a distinction is made between the various stages of hypertension and global cardiovascular risk. This paper discusses the logic underlying the refinements in the definition of hypertension. J Clin Hypertens (Greenwich). 2009;11:611-614.