Before any surgery you are evaluated and cleared for surgery by your family physician. Blood tests are done as well. consideration of any medical problems you have. If all is good then the risks of surgery are minimal.
Risks from buttock enhancement include bleeding, seroma formation, asymmetry, infection, and pain. In healthy people more severe complications are almost unheard of. This assumes you are relatively healthy and have been evaluated by a physician certified by the American Board of Plastic surgery.