PSA (Prostate-specific antigen) testing has significantly increased the number of men diagnosed with prostate cancer (PCa) and especially patients with low and intermediate risk disease. The effect of radical treatment (treatment of the entire prostate gland) in these risk groups is disputable while the risk of adverse effects, with erectile dysfunction and urinary incontinence, is not. Active surveillance (AS) has been developed as an alternative to radical treatment with the aim of avoiding or delaying radical treatment by closely monitoring for signs of tumor progression. Active surveillance is regarded as the treatment of choice for low-risk prostate cancer. Focal therapy may have a crucial role in improving active surveillance protocols for patients with intermediate localized prostate cancer. Focal eradication of the index-tumor may delay or avoid indefinitely radical treatment for this patient group while significantly reducing treatment-related side effects. Improved MRI-diagnostics and MRI/ ultrasound fusion technology have optimized tumor mapping and classification and this in turn has made partial treatment of the prostate a feasible treatment option. This study is a prospective cohort study. Patients with intermediate (high-risk) localized PCa and a visible index tumor will be treated with high-intensity focused ultrasound (HIFU). The aim of the study is to show that there is a significant effect of focal treatment on surveillance biopsies and a reduced conversion to radical treatment, without compromising survival outcomes compared to historical controls (retrospective cohort). A cohort from the more than 450 patients included in the local AS-protocol with MRI at Vestfold hospital trust since 2009 will serve as controls.