William Stewart Halsted was a pioneer of surgery in the USA and made many wide-ranging contributions, including the surgical treatment of breast cancer. He changed the training of surgeons from a disorganised apprenticeship to the residency training programmes used today. Halsted's research developed a better understanding of surgically amenable disease and a multitude of new techniques and operations. Over a 40-year career, beginning in New York and continuing at Johns Hopkins University Hospital in Baltimore, he endured a terrible struggle resulting from an accidental addiction, acquired in the course of his research. Despite this, his legacy to medicine and human health is one of the greatest left by any individual surgeon in history and remains an inspiration today.