Guillermo Mac Millan (born 1940/1941) is a retired Chilean urologist who worked at Van Buren Hospital in Valparaíso.
Mac Millan studied at the University of Chile, where he participated in heart transplantations led by Jorge Kaplán Meyer.
Using a modification of an existing technique, Mac Millan performed sex reassignment surgery on the woman's daughter.
[4] He had many patients from Argentina, where genitoplasty was at one time considered a mutilation punishable by imprisonment,[1] including Mariela Muñoz.
[3] The local chapter of MOVILH praised Mac Millan's work and called on the Chilean Ministry of Health to train more professionals in genitoplasty.