Balthasar Guersye, M.D. (died 1557), was an Italian physician who rose to high favour at the court of Henry VIII. On 7 November 1519, 'Thomas Roos of London, surgeon, was bound over in 100l. not to molest Baltazar de Guerciis, or pursue an information late put into the , till he prove that surgery is an handicraft'. As surgeon to Queen Catherine of Aragon, Guersye was naturalised on 16 March 1521–2. About 1530 he took the degree of M.B. at Cambridge University. On 9 November 1532, his services were rewarded by a grant of lands. On 20 August 1534, he obtained licence to depart into Italy with three servants, five horses or geldings, and twenty crowns of the sun, baggage, etc. He was also surgeon to Henry VIII, and in 1543 was engaged in collecting accusations against Archbishop Cranmer.