For inbound medical travelers (those coming from outside the US), high risk and complicated surgeries are the most popular reasons for travel. These include things like organ transplant, cardiovascular surgeries and procedures, oncology, fertility, and orthopedic surgery. Cutting edge experimental surgeries and treatments are likely to be offered in the US before other parts of the world and those are also big draws for foreign patients. Still other health tourists come to the US for eye surgery and dental care that Americans take for granted but are not available in their home land.
The US is also known for diagnostic medicine. Many foreigners travel to the US for access to high tech diagnostic scans and tests as well as more advanced health screenings than are available in their home country. Most then take those results home for treatment while a few will need to stay in the US to receive emergency or advanced treatments.
Domestic health travel is well established for things like cancer or disease treatment, organ transplants, and cardiac surgery. Patients will travel to the best treatment center in their region, even if it means leaving their hometown or crossing state lines. In recent years travel for fertility treatments, orthopedic surgeries such as joint replacement, and specialty treatments like gender-reassignment surgery or ongoing care for rare conditions and diseases has become more common. Americans are also willing to travel to obtain addiction treatment at some of the best rehabilitation centers in the world.
The actual list of treatments and surgeries available in the US is virtually endless.