The Westergren erythrocyte sedimentation rate (ESR) has been used for many years without any formal procedure for method validation or for quality assurance. In 1988, the International Committee on Standardization in Hematology (ICSH) (Leuven, Belgium) described an ESR validation procedure as well as a method for producing ESR reference material (ICSH reference method) in the laboratory where it is to be used. The ICSH proposal was tested in our laboratory during a consecutive period of 36 months. In this article, a new mathematical relationship between the ICSH recommendation and the Westergren method is developed, which can be easily used for method validation and/or quality assurance. A table has been made that establishes 95% action limits for Westergren ESRs based on ICSH reference ESRs from 5 through 105 mm/h. The table, derived from 36 months of data, has been tested against two new data sets and used to validate two commercial ESR methods. Analysis of outliers was performed with special attention to the mixing of whole blood samples with sodium citrate necessary for the Westergren ESR. This mixing process is best performed in a large-bore test tube as opposed to the use of the Westergren ESR tube as an aliquoting and mixing device.