PSA doubling time is an accepted tool to determine the probability that prostate cancer will or will not be clinically significant following primary treatment. However, the definition and proper use of PSA doubling time in clinical practice has become controversial. In this interview, W. Scott McDougal, MD, discusses where the controversy lies and explains when and how this measurement can (and cannot) be used to guide treatment decisions. Dr. McDougal is chief of the department of urology at Massachusetts General Hospital and professor of urology at Harvard Medical School, Boston. He was interviewed by former Urology Times Editorial Consultant Robert C. Flanigan, MD, who is professor and chairman of the department of urology, Loyola University, Maywood, IL.