In the 1960s, Ida Macalpine and Richard Hunter, mother and son psychiatrists, stated that George III's medical records showed that he suffered from acute porphyria. In spite of well-argued criticisms by Geoffrey Dean and Charles Dent based on their extensive clinical experience of the acute porphyrias, Macalpine and Hunter were able to garnish extensive support for their claims from historians, psychiatrists, physicians and the media circus and their view is now surprisingly widely accepted. Recent research of George III's extensive medical records has shown that Macalpine and Hunter were highly selective in their reporting and interpretation of his signs and symptoms and that the diagnosis of the acute porphyria cannot be sustained. The basis for the false claims and the consequences for historians are considered and indicate that there is now an opportunity to reassess George III's contributions to events in his reign.