Steven L. Simon received a Ph.D. in radiological health sciences from Colorado State University in 1985. He has served on the faculties of the University of Utah and the University of North Carolina at Chapel Hill. He spent five years directing the Marshall Islands Nationwide Radiological Study and also participated in the radiological monitoring of the former nuclear test sites@Johnston Island,  in Algeria, and in French Polynesia. Simon joined the National Cancer Institute (NCI) in 2000 and now focuses on retrospective dose estimation in support of epidemiologic studies of radioactive fallout and occupational exposure in medicine. Address: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, 6120 Executive Blvd., Bethesda, MD 20892. Email: ssimon@mail.nih.gov.