BACKGROUND: The degree of variability in prostate-specific antigen (PSA) measurements is important for interpreting test results in screening programs, and particularly for interpreting the significance of changes between repeated tests. This study aimed to determine the long-term intra-individual variation for PSA in healthy men. METHODS: A randomly selected cohort of men in a biennial prostate cancer screening program (ERSPC) conducted in Sweden from 1995-1996 to 2001-2002. We studied men who had total PSA (tPSA) levels