George III: a revised view of the royal malady

George III of England's episodic psychotic illness is described. The data has previously been used to substantiate the diagnosis of an unlikely hereditary metabolic disease, porphyria. A scientific perspective, aimed at removing psychiatric diagnosis from dependence on subjective evaluations, is corrected by the diagnosis of a mood disorder. His unipolar mania of late onset is a syndrome, the sine qua non of bipolar disorder, in this instance complicated by the toxicity of quinine, antimony, and purgatives.