Prostate-specific antigen (PSA)-based screening for prostate cancer (PCa) can reduce PCa mortality, but also involves over-detection of low-risk disease with potential adverse effects. We evaluated PCa incidence among men with PSA below 3 ng/mL and no PCa diagnosis at the first screening round of the Finnish Randomized Study of Screening for PCa. Follow-up started at the first screening attendance and ended at PCa diagnosis, emigration, death, or the common closing date (December 2016), whichever came first. Cox regression analysis was used to estimate hazard ratios and their confidence intervals (CI). Among men with PSA <3 ng/mL, cumulative PCa incidence was 9.1% after 17.6 years median follow-up. Cumulative incidence was 3.6% among men with baseline PSA 0–0.99 ng/mL, 11.5% in those with PSA 1.0–1.99 ng/mL and 25.7% among men with PSA 2–2.99 ng/mL (hazard ratio 9.0, 95% CI: 7.9-10.2 for the latter). The differences by PSA level were most striking for low-risk disease based on Gleason score and EAU risk group. PSA values <1 ng/mL indicate a very low 20-year risk, while at PSA 2–2.99 ng/mL risks are materially higher, with 4–5 -fold risk for aggressive disease. Using risk-stratification and appropriate re-screening intervals will reduce screening intensity and over-detection. Using cumulative incidence of clinically significant PCa (csPCa) as the criterion, re-screening intervals could range from approximately three years for men with initial PSA 2–2.99 ng/mL, six years for men with PSA 1–1.99 ng/mL to 10 years for men with PSA <1 ng/mL.