The salient characteristics of the Lipid Research Clinics (LRC) Program Prevalence Study are presented, including an overview of its structure, the populations included and the common procedures used. Highlighted are the two sequential screening examinations that included 68,317 participants in 12 LRCs in the U.S. Canada and the U.S.S.R. for the first examination and 15,816 for the second. Several thousand more will be added as the thirteenth LRC completes its screening in Israel. Major data items are described briefly, as are data quality enhancement procedures. Procedures for plasma lipid determination, lipoprotein cholesterol, other clinical chemistries, nutritional intake assessment, and resting and stress electrocardiography are discussed. A discussion of the methodologic strengths and weaknesses of the findings of the LRC Program Prevalence Study is also included. This paper provides a frame of reference for the individual papers in this volume.