Active surveillance and watchful waiting are almost unique to prostate cancer, and different concepts exist for the deferred treatment of prostate cancer. Watchful waiting refers to monitoring the patient for changes in disease until the patient develops tumor metastases before giving palliative treatment. Active surveillance refers to allowing deferral of initial treatment until there is evidence of cancer progression. Active surveillance is rarely performed in patients with a long life expectancy, and the criteria for selection of this case and the timing of starting treatment have not been defined. Delayed treatment is generally used for patients with low-grade (Gleason score 2-5) prostate cancer with a life expectancy shorter than 10 years. And active surveillance is now also attempted in younger, small tumor size, low- or intermediate-grade prostate cancer patients to avoid or delay treatments that may not be necessary immediately. For patients with low-risk prostate cancer, or those with advanced metastases who cannot tolerate the side effects of treatment, watchful waiting may be an option. For these patients, the risk of tumor progression must be fully understood and accepted, and close follow-up should be performed. They should be reviewed at the outpatient clinic every 3 months. The examination items are mainly rectal examinations and serum PSA, and if necessary, the follow-up time can be shortened and imaging examinations can be performed in parallel. If progression is detected, it is time to consider switching to other treatment modalities.