Background: An understanding of the natural history of screen-detected prostate cancer is essential for making appropriate treatment decisions; however, such data are few and far between Methods: We assembled a population-based cohort consisting of 12,271 men aged >65 years diagnosed with screened detected (T1c) localized prostate cancer during 1992 - 2009 who did not receive surgery, radiotherapy, or androgen deprivation therapy (ADT) within 6 months of diagnosis. Competing risk analyses were used to assess cancer-specific mortality and use of cancer-related interventions. Results: Compared to outcomes of pre-PSA era patients, 15-year survival has improved considerably for conservatively managed patients diagnosed in the PSA era. The 15-year risk of prostate cancer specific mortality for men aged 66-74 diagnosed with T1C Gleason 5-7 prostate cancer was 6.1% (95% CI 3.6-8.8% ) compared to 17 - 23% among men diagnosed in the pre-PSA era. Similarly, substantial improvement was observed for patients with T1c Gleason 8-10 prostate cancer: 15-year prostate cancer mortality was 21.4% (95% CI 11.9 – 44.2%) compared to 56-65% in the pre-PSA era. The 15-year prostate cancer mortality for patients aged 75+ was 9.8% (95% CI 7.7-12.1%) for Gleason 5-7 and 25.2% (95% CI 18.4-33.2%) for Gleason 8-10. Among patients aged 66-74 with T1c Gleason 5-7 cancer, 53.6% (95% CI 50.6 – 56.9%) received cancer therapy (42.3% attempted curative therapy, 22.5% ADT, 6.6% palliative therapy) within 15 years of cancer diagnosis. Among those who received attempted curative cancer therapy, the majority did so within the first 3 years of follow-up. Conclusions: To our knowledge, this is the largest US population-based long-term study on screen-detected prostate cancer initially treated with conservative management. Fifteen-year disease-specific mortality following conservative management among men with screen-detected cancer has decreased by more than 60% as compared with results from the pre-PSA era. The risk of death due to prostate cancer for men diagnosed with T1c Gleason 5-7 disease in the PSA era is low.