Background: Japan is participating in the Prostate cancer Research International: Active Surveillance (PRIAS) study as PRIAS-JAPAN since 2010. This study’s aim is to report the long-term outcomes of the PRIAS-JAPAN study initiated in 2010. Methods: Basic patient eligibility criteria were clinical stage ≤T2, PSA ≤10, PSA density (PSAD) <0.2, number of positive cores ≤2, and Gleason score (GS) ≤6. Those have been revised progressively since then, and since January 2021, for patients who underwent MRI fusion biopsy at the time of initiation or follow-up biopsy, PSA ≤ 20, PSAD < 0.25, and the number of positive cores ≤ 2 for GS3+3, and ≤ 6 for GS3+4. For the number of positive cores, the eligibility criteria were expanded to no limit for GS3+3 and no more than half of the total number of cores for GS3+4. PSA test every 3 months, rectal examination every 6 months, biopsy at 1, 4, 7, and 10 years, and every 5 years thereafter, and recommendation for secondary treatment after confirming pathological deterioration. Reevaluation of MRI within 3 months after diagnosis and targeted biopsy of the same site if there is a lesion suspicious for cancer, and recommends annual MRI when PSA-DT < 10 years and annual systematic biopsy if MRI cannot be performed. Results: As of the end of February 2023, 1204 patients were enrolled. The eligibility criteria were met in 1173 patients. The median age, PSA, PSAD, and number of positive cores were 69 years, 5.3, 0.15, 1, 844, and 309, respectively, and the clinical stage was T1c in 1,019 and T2 in 154 patients. The acceptance rates of re-biopsy at 1, 4, 7, and 10 years were 83.0%, 63.5%, 39.0%, and 20.3%, respectively, and the pathological deterioration rate at each re-biopsy was 29.4%, 29.7%, and 35.6%, respectively. The pathological deterioration rate at the time of each biopsy was 29.4%, 29.7%, 35.6%, and 18.1%, respectively.467 patients selected subsequent therapy and prostatectomy was the most frequently chosen treatment option. Conclusions: Pathological deterioration was observed in about 30% of patients at the time of biopsy, but the rate of biopsy decreased over time. Adherence to biopsy was considered necessary for the safe implementation of active surveillance. Clinical trial information: 2021-211.