The NCI imbedded the notion of comprehensive quality control and assurance (CQA) in the design concept for the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. PLCO implemented a comprehensive, adaptable quality assurance and control program to span more than 20 years of data collection, coordinate multiple institutions and committees, and integrate a wide variety of complex protocols. CQA concepts, practices, and procedures traced through all aspects of trial management, governance, and operations of PLCO. The driving force behind CQA in PLCO was scientific and clinical credibility of trial data and findings. CQA as implemented in PLCO was operationally analogous to the concept of Total Quality Management (TQM) described in the management literature. This paper describes CQA actualization in PLCO.