The decision analysis technique has been used to estimate the benefits of treatment strategies for a variety of diseases. This analysis demonstrated that a selective treatment with a reasonable specificity and sensitivity for detecting clinically significant cancer is more beneficial to the patients with T1c cancer under 70 years of age than radical prostatectomy or watchful waiting assigned to all patients. Moreover, it was clearly indicated that quality-of-life (QOL) is the most important factor for deciding the optimal treatments of prostate cancer.