Prostate cancer (PCa) remains one of the most commonly diagnosed malignancies in men worldwide. Early diagnosis and definitive therapy seem to improve oncological outcomes in men with high-risk disease, but significant concerns exist in terms of the overdiagnosis and overtreatment of patients with lower-risk tumors. In this context, active surveillance (AS) has recently emerged as a alternative treatment strategy in PCa patients with low risk cancers. However, published data are based on Western population with different protocol, and therefore; well-controlled data with well-organized and prospective cohort are urgently needed in Korean patients with low-risk PCa because Korean patients have significantly different tumor characteristics compared to Western patients. Here, the investigators have a plan to establish the Seoul National University Enrolled Registry for Prostate Cancer with Active Surveillance, and finally provide the concrete evidence for the clinical outcomes of active surveillance program as the primary therapeutic strategy for low-risk PCa in Korean men.