Purpose: Previous studies have examined the relationship among prostate specific antigen, other predictive factors and current prostate cancer risk. We examined the population risk during 4 years, defined a prostate specific antigen associated with this risk and clarified the contribution of other predictive factors. Materials and Methods: The population consisted of men 55 to 70 years old screened at the first and second screening rounds 4 years apart in the Rotterdam Section of the European Randomized Study of Screening for Prostate Cancer. The proportion of men with a positive prostate biopsy (initiated for a prostate specific antigen of 3.0 ng/ml or greater) and the mean population prostate specific antigen were calculated. Multivariate modeling was conducted using a proportional odds regression model to establish significant predictors of a positive biopsy from round I to round 2 of screening. Results: Among men with no previous prostate biopsy the 4-year risk of prostate cancer was 5.1%, which was associated with a mean prostate specific antigen of 1.5 ng/ml at the first screening. An increased prostate specific antigen was a highly significant predictive factor for biopsy detectable prostate cancer 4 years later. Increasing log total prostate volume and a previous negative biopsy were associated with a significant reduction in risk of a positive prostate biopsy 4 years later. Conclusions: A prostate specific antigen of 1.5 ng/ml or greater in men older than 50 years represents an indicator for greater than average future risk of prostate cancer. Prostate specific antigen and other factors can be used to define future prostate cancer risk in addition to current use as a diagnostic marker for prostate cancer.