Active surveillance (AS) or watchful waiting is a management option for localized prostate cancer that can be offered to appropriate patients who would also be candidates for aggressive local therapies (surgery and radiotherapy), with the intent to intervene if the disease progresses. This distinguishes AS from watchful waiting, another observational strategy for men that would not be candidates for curative therapy (surgery, radiation) because of a limited life expectancy. AS offers men with a prostate cancer that is thought to have a low risk of causing harm in the absence of treatment, a chance to delay or avoid aggressive treatment and its associated side effects.