John Thurnam (28 December 1810 – 24 September 1873) was an English psychiatrist, archaeologist, and ethnologist. In 1846 he was appointed Medical Superintendent of The Retreat, the Quaker psychiatric hospital near York. In 1848 he reported two maternal first cousins with an unusual condition affecting the skin, hair and teeth (an ectodermal dysplasia); he had performed an examination post mortem on one of the two men, including relevant histopathology.