Debate is ongoing about the treatment of organ-confined prostate cancer, particularly in men who have low-risk disease detected by PSA screening. A balance is needed between the harms and benefits of treatment. New techniques are being developed that aim to offer similar treatment effects to current radical therapies, while reducing the associated harmful effects of these treatments. In this Review, we explore the potential of one such technique, photodynamic therapy (PDT), for the treatment of organ-confined prostate cancer. PDT uses a photosensitizing drug that is activated in the prostate by low-power laser light, delivered using optical fibers. The fibers are placed within needles in the prostate, guided by transrectal ultrasound and a perineal template. Following the activation of the photosensitizer by light, and the formation of reactive oxygen species, necrosis occurs at the site of interaction between the photosensitizer, light and oxygen. Clinical studies are underway to investigate the use of PDT for primary and salvage treatment of organ-confined prostate cancer. We review these studies, the potential strategies for enhanced photodynamic effects, and the current limitations of PDT for prostate cancer.