The author describes one case of idiocy combined with athetosis, and gives a summary of the contributions which have been made to this subject. The number of autopsies of double athetosis is small. The lesions found in athetosis have been mainly of a hæmorrhagic character, though a few cases of atrophy and asymmetry of the brain, cerebellum, and bulb have been recorded. Athetosis is not infrequently met with in paralytic idiocy, although it often occurs where the intellect is not impaired. It seems needless, therefore, to treat what is merely a symptom of cerebral or nervous irritation as a concomitant of so profound an affection as idiocy.