Although high-intensity focused ultrasound (HIFU) has fewer side effects than many other treatments for prostate cancer, that doesn't mean it doesn't have any.
After HIFU, you may have trouble getting an erection, but this usually goes away in time and there are drugs that can help you while you regain your ability to do so. Some men also have trouble peeing or may leak urine between trips to the bathroom.
Other side effects may include pain between your testicles and your rectum, which can often be handled with medication. There's also a risk for blood in your urine, a urinary infection, and an infection in your testicles. Always call your doctor right away if you have signs of any of these.