Background: Long-term psychological well-being and quality-of-life are important considerations when deciding whether to undergo active treatment for low-risk localised prostate cancer. Objective: To assess the long-term effects of active surveillance (AS) and/or watchful waiting (WW) on psychological and quality-of-life outcomes for low-risk localised prostate cancer patients. Design, setting, and participants: The Prostate Cancer Care and Outcome Study is a population-based prospective cohort study in New South Wales, Australia. Participants for these analyses were low-risk localised prostate cancer patients aged <70 yr at diagnosis and participated in the 10-yr follow-up. Outcome measurements and statistical analysis: Validated instruments assessed outcomes relating to six health-related quality-of-life and nine psychological domains relevant to prostate cancer patients. Adjusted mean differences (AMDs) in outcome scores between prostate cancer treatment groups were estimated using linear regression. Results and limitations: At 9–11 yr after diagnosis, patients who started AS/WW initially had (1) higher levels of distress and hyperarousal than initial radiation/high-dose-rate brachytherapy patients (AMD = 5.9; 95% confidence interval or CI [0.5, 11.3] and AMD = 5.4; 95% CI [0.2, 10.5], respectively), (2) higher levels of distress and avoidance than initial low-dose-rate brachytherapy patients (AMD = 5.3; 95% CI [0.2, 10.3] and AMD = 7.0; 95% CI [0.5, 13.5], respectively), (3) better urinary incontinence scores than initial radical prostatectomy patients (AMD = –9.1; 95% CI [–16.3, –2.0]), and (4) less bowel bother than initial radiation/high-dose-rate brachytherapy patients (AMD = –16.8; 95% CI [–27.6, –6.0]). No other significant differences were found. Limitations include participant attrition, inability to assess urinary voiding and storage symptoms, and nonrandom treatment allocation. Conclusions: Notwithstanding some long-term differences between AS/WW and various active treatment groups in terms of distress, hyperarousal, avoidance, urinary incontinence, and bowel bother, most long-term outcomes were similar between these groups. Patient summary: This study assessed the long-term psychological and quality-of-life impacts of initially monitoring rather than actively treating low-risk prostate cancer. The results suggest that initial monitoring rather than active treatment has only a minor impact on subsequent long-term psychological and quality-of-life outcomes. The results of this study suggest that initial monitoring rather than active treatment of low-risk prostate cancer has only a minor impact on long-term psychological and quality-of-life outcomes.