• Department of Public Health Sciences, Henry Ford Health System, Detroit, MI USA. llamera1@hfhs.org.

The most rigorous and accurate approach to evaluating clinical events in cancer screening studies is to use data obtained through medical record abstraction (MRA). Although MRA is complex, the particulars of the procedure-such as the specific training and quality assurance processes, challenges of implementation, and other factors that influence the quality of abstraction--are usually not described in reports of studies that employed the technique. In this paper, we present the details of MRA activities used in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, which used MRA to determine primary and secondary outcomes and collect data on other clinical events. We describe triggers of the MRA cycle and the specific tasks that were part of the abstraction process. We also discuss training and certification of abstracting staff, and technical methods and communication procedures used for data quality assurance. We include discussion of challenges faced and lessons learned.