10017 Background: It remains unknown whether more intense prostate cancer screening and treatment reduces prostate cancer mortality. We describe the experiences of two population-based cohorts with 15-years follow-up (1987–2001) to address the following questions: 1) does more intense screening and treatment for prostate cancer lead to lower mortality in community settings, and 2) do older men (age ≥75–79) benefit from more intense prostate cancer screening and treatment. Methods: Population-based cohort study consisting of white male Medicare beneficiaries who resided in the regions covered by the Seattle (N=88,863) and Connecticut (N=114,785) cancer registries. Inclusion criteria are age 65–79 and free of prostate cancer on January 1, 1987. All study subjects were followed through death or the end of 2001. The main outcomes are rates of screening for prostate cancer, treatment with radical prostatectomy, external beam radiotherapy, and prostate cancer specific mortality. Results: Between 1987 and 1990, compared to men in Connecticut, men in the Seattle region were 5.4 times (95% C.I. 4.8 - 6.1) more likely to undergo PSA testing, 2.2 times (95% C.I. 1.8 - 2.7) more likely to under go prostate biopsy, 5.9 times (95% C.I. 5.5 - 6.9) more likely to have radial prostatectomy, and 2.3 times (95% C.I. 2.2 - 2.5) more likely to have external beam radiation. The cumulative risk of radical prostatectomy or external beam radiation reached 9.1% in the Seattle cohort and 5.0% in the Connecticut cohort in 2001. After 15 years of follow-up, prostate cancer mortality rates were similar for subjects in the two study regions (hazard ratio of Seattle to CT: 1.01, 95% C.I. 0.93 - 1.09). For older men (aged 75–79 in 1987), however, the prostate cancer mortality rate was slightly higher in the Seattle than the Connecticut cohort (hazard ratio: 1.16, 95% C.I. 1.02 - 1.32). Conclusion: More intense screening for prostate cancer, surgery or radiation among a cohort of Medicare beneficiaries in the Seattle area compared with their counterparts in Connecticut has not lead to significantly lower mortality from prostate cancer over 15 years of follow-up. No significant financial relationships to disclose.