Prostate cancer is the most common cancer in men. Because these tumours are usually detected by early diagnosis, prostate cancer is often limited to the prostate when diagnosed. Withholding active treatment, with active surveillance or watchful waiting are full options for men with this diagnosis. In active surveillance, men receive a structured follow-up with repeated determinations of the prostate-specific antigen (PSA) and prostate biopsies, often supported by MRI. When the tumour develops, active treatment can still be initiated. With this approach, the 10-year survival rate is high and a significant proportion of men remain untreated. With watchful waiting no structural monitoring takes place; instead one waits until the prostate cance...