William Pitcairn (9 May 1712 – 25 November 1791) was a Scottish physician and botanist. He was born in Dysart, Fife, the second son of the Revd David Pitcairn. A younger brother was John Pitcairn, who became a British Marine officer and was killed at the Battle of Bunker Hill; John's son and William's nephew was midshipman Robert Pitcairn, for whom Pitcairn Island is named. William Pitcairn studied first at the University of Leiden and then at the University of Rheims, where he was awarded his MD. He then sent to England and obtained a second degree in medicine from Oxford University in 1749.