Postoperative encephalopathy with choreoathetosis is a serious neurologic complication of childhood cardiac surgery. An inadequate understanding of the long-term outcome has limited family counseling and the institution of intervention strategies. Our objective was to define the long-term neurologic, cognitive, and behavioral outcome in this group of patients. By retrospective review we identified all cases of choreoathetosis in our cardiac intensive care unit from 1986 through 1995. During this decade we described a sudden transient increase in postoperative choreoathetosis that disappeared as we modified treatment strategies in perioperative care. These children underwent a comprehensive battery of neurologic, cognitive, and behavioral tests to determine in detail their long-term outcome. Of the 36 cases identified of which three were deceased, four were abroad, and eight were lost to follow-up, 21 families were approached, and 15 of the 21 (71%) consented to testing. We found pervasive deficits in memory, attention, and language, with a median full-scale IQ of 67 (range = 40-122), as well as in motor function, including persistent dyskinesia in seven of 15 (47%). The pervasive and enduring cognitive and motor deficits in survivors of postoperative choreoathetosis caution for guarded predictions of outcome and highlight the need for careful neurologic and cognitive evaluation in all children with choreoathetosis after open heart surgery.