Twenty-five patients convalescing from Sydenham's chorea were contrasted by clinical examination, electroencephalograms, and psychometric and psychologic tests to 15 siblings and 20 matched rheumatic fever controls. A group of 10 postchoreic patients who had two or more signs could be identified. Patients in this group had all the signs classified as moderate or severe, performed less well than other choreic subjects on the Bender gestalt test, and had a higher percentage of abnormal electroencephalograms but not a higher incidence of behavioral disorders. This subgroup could not be predicted from a review of neurologic history or from analysis of the acute episode of chorea. Our data would suggest that uncomplicated Sydenham's chorea is not necessarily a benign self-limited affliction of the central nervous system and that some patients are left with definite, albeit minimal, neurologic residua.